i own a 20' halmark, with the car inside of it ti weighs 7,00 or so , i had a f-250 03' off the lot, great truck, but not fun to drive every day on rough roads and it cost too much for me, i decided to get a 02'f-150 ext cab, tows my trailer just fine, and it only with a 4.6 v8, i used to pull the trailer with a 92' short box reg cab f-150, and it towed it just fine, no prob with tires, front tire loading or anything else, i pulled with all the above from NC to NY, though the mountains of pa and i usually kept a 60mph pace, could yank it to 70 if i wanted to, it was a little slower in the mountains but never below 55, so the way i see it is what ever you want, get, but remember that you dirve the truck a whole lot more without a trailer than you do with, so you might be happier with a truck that can pull the trailer and keep some money in you pocket to play with, rather than have a truck that can pull a 40ft trailer and less play money, if i can pull 800 miles with a 5.0 or 4.6, then i think anyone would be fine with the same, the only thing i recomend is brakes on both axles of the trailer, you can never stop fast enough. i drove small wreckers for a few years, those things with a lincoln on the back are nose light and dangerous, and they have no extra brakes on the towed load, so in retrospect the trailer is way way safer with brakes.
grant