1999 Tahoe z71 with no Guts

I decided to buy a clean older vehicle just for pulling my 2000lb Alumacraft 165 Classic CS. I used to own a 2001 GMC Yukon XL and it was an awesome tow vehicle.

I found an extremely clean but high mileage 1999 Tahoe z71. To my surprise, this thing feels like its towing a 10,000lb travel trailer with my little 2000lb rig!

It has oversize tires....could this be the problem? I ordered a Superchips tuner and hope it will help with the power and shift points.

How do other comparable Tahoe/Yukons do towing your rigs?

I also have a 99 tahoe z71, mine has a little over 210,000 miles on it. My Tahoe has no problems with a trailer. Last week I towed 2 yards of pea gravel for 30 miles and it pulled no problem. I have a trailer hooked up 6 days a week, sometimes carrying a couple hundred pounds and sometimes a couple thousand.

Long story short my Tahoe pulls great.

Tires may have something to do with it but i doubt it will effect it much. Does it have 3:42 gear ratio or 3:73. 3:73 are a better ratio for pulling but 3:42 are better for highway driving.

And tuners on gasoline engines dont justify enough performance upgrades to make many improvements. The naturally aspirated engine can only breath so much and your not adding any fuel so you wont see much improvement. It may change shift points but its not going to give you the torque where you need it.

And also a tuner on a high mileage vehicle your just asking for problems.

Not trying to sound harsh just giving you the facts.

I expected that!....something not quite right with mine.

Thanks for the reply!

I have 2 Z71 trucks. One is a 98, the other is a 97! Z71 is a suspension package. Is it 4wd? If so then you should have 3.73 gear ratio. They pull really good! Try putting the right size tires on if possible. By the way, My 97 is pushing 300,000 miles and I have driven to Falcon twice and to the coast twice a year! Its possible you could have a stopped up cat. They have 2 cats, and one could be your culprit! Lets us know!

I have 3.73 gear ratio and 4 wheel drive. I'm still thinking its the tires. It's a shame because they are brand new before I bought the car 2 weeks ago...plus they look great!

I'm hoping the tuner will let me change the shift points because it's in high gear in flash right now. You have to really mash it to get it to go...once at speed it's pretty sweet. I pulled my boat to Ray Roberts Sat and again on Sunday...got 14.4 mpg at 65mph...not bad?

No codes but I'm going to have the cats checked. I had that happen on a Yukon XL that I used to own and it just sucks the life out of the engine. Thanks for the reminder!

For that rig 14.4 at 65 aint bad at all. And im sure your thinkin about this but i will give my 2 cents as far as air filters. I dont believe in k&n. they claim better mpg and more power. The only way possible to do this is take away restriction to make it easier for the engine to breathe. And the only way to do that is less filter media. To me its not worth the extra mpg or power you MAY POSSIBLY get to sacrifice the engine. Run a quality filter. Oem is great and you cant go wrong with wix.

However exhaust systems do seem to make some difference. But again maybe not enough to make big improvements.

What size tires are they? My tires are also bigger then stock but i have no issues towing.

I think you have something else going on. Is your exhaust smoky? Maybe you have a fuel or spark problem. How does it run with no trailer?

285/75/16 and 2" lift by the previous owner. I asked him about performance before and after and he said the change made a negative difference but it wasn't that bad to him but he never pulled a trailer.

Mechanically its all good even though it's got 220,000 miles. New fuel pump, throttle body and injectors recently cleaned and flushed. New distributor cap, wires and plugs. It doesn't use oil between changes.

It feels like the parking brake is on and she's working all the time. This is with and without the trailer. Once she's up to speed all is good until I need to pass somebody or go up a hill.

285 tires and with 3:73 gears is the proper ratio.

if your Yukon had 4:10's with a 6.0 it may make a difference.

I would say your tires and axle ratio are not the problem

what engine btw?

350 or the 305?

350 in the current Tahoe and in the 2001 Yukon XL that I used to have.

There will be a difference between the two. Your 99 has a 5.7 350 V8. The 01 Yukon will have the 5.3 327 V8.

So the old Yukon was towing stronger with a smaller engine?...that's depressing! I assume that the 350 should be a stronger runner?

My 1/2 ton 5.3 out pulled my 3/4 5.7 everyday of the week. And got 6 mpg better while doing it.

The 5.3 is a strong engine. I had a 99 Silverado with the 5.3 and it pulled my boat great. I got an honest 15mpg towing a 19' boat with a 200. I think the 5.3 came with 305 horsepower, while the 97-99 5.7s had 285 horsepower.

Maybe you are having transmission problems? Your Tahoe should pull just fine.

Fuel filter or cat converter restriction

I gotta disagree with that. I have a 2011 5.3 and for towing preferred my 350. Sure the 5.3 make more hp and torque, but it makes it at 5500+ and 4500+ RPM. My 350 didn't make near as much Hp and was closer on torque, but it made max hp at 4000 rpm and max torque at 2400 rpm, right where the rpm's fell pulling in 3rd gear. I will not tow a 4000 rpm... therefore all the power it makes at 5500 and 4500 rpm is pretty useless.

I agree with redchevy. I had a 5.7L Yukon, and 5.3L Yukon.. The 5.3L ran as good as it could, but to me "felt" like a dog. It would barely break the tires loose on a hard acceleration.. the 5.7L "felt" like a hoss and would burn the tires off if desired. The gearing was the same on both.
So now I drive a 7.3L Ford Diesel with 500hp and 650lb ft of torque. I love it.

Another thing I thought about.... I have my own shop. I have seen countless older cars and trucks that come in with no CEL that has a problem. A lot of folks will simply pull the bulb out to just sell the vehicle! I would still check for codes or at least have someone (that you trust) to look at the data on the pcm!

Installed the Superchips tune this afternoon and used their default settings for the "Towing" option tune. It also let me correct for the larger size tires.

I'm very impressed with the difference! With the trailer, I could definitely accelerate to highway speeds quicker and it would hold speed much longer on hills before downshifting. In between it runs extremely smooth. It will be interesting to see what happens to the fuel economy on my next trip to the lake this weekend!

The only negative is that I'm supposed to start using 91 octane. Worth it to me to see the motor not having to work so hard!

Much Much Better!

Make $$$$ sure if it says run 91 octane you do! In the shop i work in we recently replaced all 8 pistons in a 5.3, 4 of which were broke. The truck had a tuner on it, i cant say they didnt run 91 octane but im pretty sure they didnt.

Before i started at this shop they replaced a piston in another 5.3 that the piston crown was melted all the way down to the first compression ring. And it was confirmed that this engine was not run on 91 octane.

Thanks for the heads up!....Will do!!

You can disagree all you want, I'm the one that owned them. Was the 5.7 a dud? Maybe. Was the 5.3 one of those special ones made that I rarely get? Maybe.

Good luck with the chip, but I'm not sure you'll get better mileage and you didn't know the true mileage anyways since the tires weren't accounted for before the chip. Keep us informed though, I've never read about the gasoline chips.

Actually I did alter the mileage distance by 3.7% to account for the larger tires when I figured the mpg.

I've only owned this car for three weeks so I haven't run many tanks thru it to see a true average.

Good deal. Most people just look at the odo, do the gallons and don't take the time to really calc it out like you were doing.

I am shocked that a tuner fixed your issue.

Mine is bone stock and tows great.

I was surprised too! I think the oversize tires were the real issue because everything checks out mechanically.

The tuner was cheaper than replacing the almost new tires. I think changing the shift points made the biggest improvement and it must have advanced timing a little because of the requirement to start using 91 octane?

I'll get some miles on it and report back.

You really ought to replace that cup of piss in your cheerios with milk

Oh sorry, I guess I failed to see since you owned my 2 trucks that you were qualified to disagree with me.

By the way, I don't eat Cheerios and I don't drink piss so you can keep both.

I'm guessing that 3/4 ton may have weighed a little more, possibly affecting mileage and performance?

GM has had their transmissions programmed to upshift too early for a while now in my opinion. I think its all part of the quest for more mpg's. Couple that with bigger tires and it probably is a lot of your problem, hope it all works out for you.

SOUNDS LIKE SOMETHING IS GOING ON. PLUGGED CATS??