I guess we are talking about a 235 and the 3.38 gears. You are absollutely correct in that you feel less torque. The rear ratio is a torque multiplier, and 3.38 is much less of a multiplier than 3.90. That being said, a 235 in good shape should not have any problem pulling the 3.38 gears, but it might not do it in record time. If you are having deminished capacity, or lessoning performance, it may be something as simple as timing or valves out of adjustment, or something more serious like low compression from worn rings. More inforrmation is needed. Have you done a tune up? Compression test? Adjusted the valves? Poor performance can also be from lower quality gasoline, stuck float in the carbuerator, clogged fuel or air filter, or even points that are out of adjustment.
The factory put 3.90 gears in your truck because it transmitted good torque and acceptable fuel economy for the time. I wouldn't expect your truck to be a rocketship with higher gears.
