Looking at buying a used F250 for towing an RV when I retire. Gas or Diesel? Pros/Cons?

Depends on how big of an RV and how far you want to tow it.

16-20ft. Trips to different states. Why would distance make a difference?

You will get lots better mpg with a diesel, however, diesels are expensive to maintain. I have both and my gas rig is a F350 with the 6.2 gas engine. The 6.2 is a stout engine for a gas rig. The diesel will cost you more up front, the fuel is a little more expensive and the filters are very expensive. We won't even mention the cost of any parts you might have to buy. The diesel of course will out pull the gas rig and if you're going through mountains you will appreciate that. The initial cost of the gas truck is several thousand cheaper as is the upkeep and the fuel is a bit cheaper. The mpg is less but you can buy a lot of gas before catching up to the extra money you would spend on a diesel. Hope this helps.

Yes it does, thanks.

Well even with a big RV shorter trips would be just fine with the gasser. If I was pulling long distances with a heavy RV I would want the diesel. If I was only pulling an 16-20' RV I would buy a Toyota Tacoma.

If you want power, longevity, better mileage, and better resale, go with a diesel.

I darn sure wouldn't buy a Tacoma but it would be a 1/2 ton.

There is absolutely no need for a 3/4 ton truck with a 16-20 foot travel trailer, you would be throwing money away.

im sure you may know this but stay away from the 6.0 powerstroke unless its bullet proofed. The 6.4 powerstroke is a alright motor once everything is deleted on it. The 7.3 powerstroke is a super good and reliable engine. The 7.3 will hit 300,000 miles easy. The only thing with the 7.3 is that its slower compared to the 6.0 and 6.4 and 6.7. By the way the newer 6.7 powerstrokes are alright but the problem with almost all diesels today is that they are choked down. The 7.3 doesn't have much emission stuff on it. I drive a 2002 f250 7.3 with 120,000 miles and have had no problems. The gas motors are not bad but once you load them down the mpg sucks on them. Id go diesel but like everyone else said, the repairs on a diesel cost double the repair of something on a gas engine.

The emissions control alone is reason enough to not get a diesel for that load. Your not going to be working it hard enough to even tax a modern 1/2 ton much less need a heavy duty diesel.

16-20ft? Plenty of 1/2 tons that will accomplish this easily.

Neither is a good thing.

but true

gas engines have 300.00 uh ohs
diesel engines have 3000.00 uh ohs

My Tacoma is great for towing heavy for a 18' bass boat but you have to consider the wind resistance on a RV of the same weight. The wind resistance is like adding another 1000 lbs. I remember towing FILs pontoon and while quite a bit lighter than my boat it towed like much heavier.