Towing to the track

the 350 chevy when towing doesn't get better mileage then a 454 when towing. For just summertime towing I would recommend a 2wd. They get better mileage and will be almost 1/2 the price of a used 4x4. Towing my Barracuda back from Seattle on a u-haul trailer my 99 454 4x4 suburban got 11 mpg and we went 65-70mph and you gain 3500 feet of elevation along the way. We have gotten rid of the suburban and now have a duramax which does much better but they ain't cheep. Your best bet for tow rig on the cheep would be a mid 90's 2wd 454 chevy. The 96-99 are vortecs and are a bit better but the lower cost of an eariler one may more then offset whatever the gains may be. I just sold a 96 Silverado crew cab long bed 454 2wd for $3100 with 125k on it. I don't know what kind of mileage it would get because it got 11 mpg towing but had a flat lobe on the cam. We put the new cam in it and sold it before having the chance to check mileage. The new cam certainly made the truck more powerful then it had been.
Diesels might get better, maybe 16 towing (some guys claim 20 towing but usually they have 1000's in mods and likely their numbers stretch the truth some) but you also have to consider diesel gas costs more per gallon and you'll pay $10,000+ for a used cummins.
something like this for $1250 might be pretty sweet.
http://seattle.craigslist.org/tac/cto/3045076673.html