Get an early Excursion with the 7.3 PS diesel and be done with it. (10000 pounds)

George

I have a Chevy HD 2500, all set up for towing- 6.0 V8, 4:10 gears, locking diff, tranny coolers, big brakes, yada yada...

I get about 13 mpg when towing heavy loads, and about 13 mpg when the truck is empty.

I pulled my 5000# boat with my quad.
Not far either mind you.

T,
2500#s seems light for a 21' boat? Is it a fishing boat or what?
Anyway, I agree, you should be fine.
I've towed boats all my life with...... well you don't wanna know!
Cheers

My wife's Montero Sport with a V-6(3.5 liter)pulled my integra on a dolly(which was loaded with tools and what not) and had the back of the truck loaded with TV and stereo equipment from Houston to Sacramento. I averaged almost 20 mpg running in D3 or whatever, not overdrive. It did a lot better than I expected, plenty of torque and a limited slip will help a lot. You definitely want a posi or limited slip for pulling a boat. Definitely get a transmission cooler, maybe one for the differential too, or at leasted finned cover to radiate heat better.

My father-in-law has the bomb diggidy GMC, turbo diesel, 6 speed, loaded. It is a beast, but a mighty nice truck, nice leather upholstery. Crew cab, long bed. Runs mid 16's in the quarter, mid 17's with a ton of weight in the bed.