I had a similar issue with my prop(25p Fury) , played with the plugs and nothing. Removed all the plugs and made all the difference.

I'm wondering if a hydraulic jack plate would help.

You added a lot of weight, is it hot and humid there also? If so no motor will run its best when its hot and humid. Doesn't have to be real hot, the humidity alone will kill the power. And a Merc is worse than the new Yamaha's. Ask any drag racer what moister in the air does to motor power. Don't believe the guys that say its hot water, it's the air.

70 degree water/100 degree air temp. The previous owner ran the same water and hit mid seventies. I'm thinking its prop, jack plate, drag.

check prop pad height and adjust 2.5-3" below pad i bet your sitting to low

Do I measure the 2.5"-3" from pad to cavitation plate?

center of the bullet or prop shaft.

No.

First get the boat level. Use a long carpenters level held on the bottom of the pad as close to center as possible. Have someone crank the tongue jack while you hold the level. Take off the prop. Once the boat's pad is level now trim the motor until the prop shaft is also level. Now measure the difference from the center of the prop shaft to the bottom of the pad. It's kind of a pain for probably not much gain.

To answer your question about a hydraulic jack plate. Yes, it will help but probably not as much as you think. The hydraulic jack plate will allow you to adjust your engine height on the fly to get the maximum performance from your boat with the load you have in it at that time.

The less weight you have in the boat, the higher you can run the motor. The more weight, the deeper the prop will need to be to lift the hull free of the water. It's all about drag, aerodynamics, humidity, water temp, etc.

I've been down this road about 15 times trying to eak out the last few .07 mph from my boats. I finally get my Bass Cat or Triton or Ranger running to my liking and a guy in a Bullet or Allison comes running by me like I'm tied to a stump....

Through the years, I've owned a few Bullets & Allys too. Then you want them to run to their optimum potential. Then you spend $5K working the lower units, buying exotic props, having the bottom of the boat blueprinted, milling the heads on the motor, etc. I've owned five bass rigs that would run in excess of 100 lightly loaded. Not to boast. I'm back in a Legend/Yam 250 SHO that runs 68 mph loaded down to fish.

Weight distribution in your boat can have a big effect on top speed as well. Make sure you have all the heavy stuff in the rear of the boat. If you are loaded heavy up front in your boat it can cost you 3-5 MPH. The trade-off is, the more weight you have in the rear, the slower your holeshot.

My suggestion is, save the $$ and keep the stock jackplate. If you start down the road of chasing the last few tenths of MPH in your rig, it can get REAL expensive in a hurry!! This is experience talking to you.

Thanks for the detail on that. I've been doing this a long time. I used to be on with skeeter and ran a new one each year. I've never worried too much about top end as long as it was close. In the case of this old boat it seems like I'm atleast 5-7 mph slower than it should be.

One thing I forgot to mention is that it wants to porpoise when I'm coming off pad fully trimmed down. Weird thing is that it only happens with the 4 blade. It looks like I'm "that guy" who doesn't know how to drive a boat....really weird.

You have a cylinder that isn't firing. That's why its down 5 mph. I had the same problem one time. I also have a Triton TR21. For best top end use a 26P Tempest plus or a Fury 26P. Quicker holes hot... loaded in the summertime a Tempest 25P. Ken is right, put the heavy stuff in the back of the boat. As far as your problem, I think you have a cylinder that isn't firing. Seen it many times.

this, in addition to the extra weight. Can make a big difference. I salivate thinking about top end in cooler weather.

Someone was just asking about their Gambler setup. If you go to www.bbcboards.net and go down to the Triton section, there is a ton of info on setups. There is also a Setup section too.

I used to have a tr196/200 opti.

It ran a 25p fury best, or a 27p tempest was my best for speed but a dog out of the hole. The aforementioned cylinder loss is a possibility because it should eat up a 24. I also liked a 25 trophy but it wasn't as fast. Best I did was 74.9 gps just me, ~half tank of gas and normal amount of tackle. I tweaked the setup a lot but no reason yours shouldn't do that or a couple more.
If you have a 6" JP, get 2" more setback. It's like a different boat. Crazy change in lift at full throttle.
2.5 prop to pad to start and make sure you know how to measure it. When I got the boat it was like 4.5 under the pad and slow. As Already given but you'll find a lot of info on bbc.

AND!!! last but definitely not least, your boat needs to be driven. You'll know it when you know it but not before. Read about chine walk on bbc, plenty of info there to read and it takes seat time beyond that. One day it will just click. If you can drive the boat full throttle and take your hand off the wheel for more than a couple seconds you have major setup problems or dead cylinder.

I'm gonna take it in and have the engine checked. I had it checked in the spring but who knows. The weight is balanced right and loaded light anyway. I've been thinking prop/jack plate. Maybe it is the motor.

You said your were getting 5600 to 5800 rpm's depending on the prop. There's nothing wrong with the motor.