i have the 87 4runner w/ 22re and 5 sp. stock gears and 32" bfg muds. i tow app. 2800 lbs. (6x12 single axle enclosed trailer, suzuki quadzilla and trx 450 quads + gas and gear) up and over the grade from sd to glamis ( 4400 foot pass w/ 6%-ish rise) every other weekend or so- no problem. the truck is rated at 3500 lbs. (2000 for the auto) towing capacity.
i usually hit it at about 55 mph in 3rd gear. it pulls fine in 4th on the flat.

forget about your mpg- if that is your concern then buy a 1/2 ton or something.... i get about 9-11 mpg with this setup.

oh and also- make sure your vehicle is in better than dd condition- i.e. cooling system, belts, hoses, brakes etc.... buy toyota parts- not kragen, auto zone pepboys junk- toyota parts!!