I just put 2300 miles on a 31 foot long motor home with a fuel injected 454 w/4L80E transmission and 4.11 gears? (about 2100 rpm @ 60 mph), had no problem on the flat hitting 85 mph when passing.
I figure the rig weighed in at around 14000 lbs which should be a bit more than a 3/4 pickup + 2 horses in a trailer. Coming up Teton pass with a 10% grade, ran nice at about 30 mph in 2nd gear. Cut back to 5% grade and did 60 mph in 3rd running about 3000 rpm. Averaged about 10mpg for the whole trip and I did not drive it easy. Fuel injection and a 4 spd tranny is the way to go if you are looking for towing torque and economy.
