I pulled a 2500# Datsun and 2500# of tools and car parts with my 48 Chevy 1/2T from San Diego to Seattle with the 235, SM420 and 4.10 gears with 235x70x15's. Top speed was 55-60. And the hills meant 3rd gear at 35mph (up and down hill, didn't trust the huck brakes with that much weight). Gas mileage was 11-12 mpg the whole trip, and she didn't drink a drop of oil, even through the Sacremento Valley in May when temps were around 90-95. Made the trip in 2 1/2 days, but my 48 has twin tanks (the 48 under bed and a 50 behind the seat), so gas stops were not too often, just a bit more pricey. :-)
Hope this gives you a few ideas. I would get a SM-420 for any towing duties, as a friend had a 60 with 235 and 3 speed that he blew up 4 3spds just pulling a 2200# utility trailer around WA state and that was with a bone stock 235...
Garry K
