BIGGY,
I have a 66 stepside with a 230 engine. I can still run the highways
very easy at 60 mph, with the stock drivetrain (3 speed column-shift non-overdrive transmission and 3.73 rear gears). I've driven trips of 50-75 miles on the interstate at 65-70 without any problems, though this is
really pushing the limits of the inline 6. At 60 I'm turning about 2850 rpms.
You
must be running either a 4.11 or 4.56 gears. Those are horrible gears for cruising. Find a 3.73 or 3.55 chunk and change it out. If you have a "Dana" rear end then 4.11 may be as high as you can go. Then your only solution is an overdrive tranny.
I'm finishing up my 292 project and I'm mating it with a GM 4-speed overdrive transmission. So I should cruise at 70 on the interstate.
