I was a Chrysler service rep when those trucks were new; sold as the Ram "Miser". The automatic version was marginal, and the 4 speed (3 + overdrive) was pitiful. However, they had extremely tall rear end gearing (2.70), which was one of the main causes of the gutless performance. This was also near the end of the line for the slant, as emissions with carburetors had sucked what life there was out of these engines.
If it is an O/D trans, a rear end swap would wake it up a bunch without destroying fuel economy. Also helps to have a properly working carb.
Even if you do swap to a v-8, you need to do something about that differential.
Mark