You should have a look at this guide for troubleshooting TBI systems.
http://www.73-87chevytrucks.com/techinfo/TroubleshootingTBISystems.pdf
The rpm changes you are seeing usually denote a vacuum leak of some kind, especially since the problems are at a lower rpm and disappear at higher rpms. Check the large potential vacuum leaks like the brake power booster and the pcv valve by blocking those items off with vacuum caps to test them, this will quickly tell you whether there is a problem with those items.
Check and reset the IAC valve. Replace the EGR valve if hasn't been replaced yet. A bad EGR will cause rough running at or near idle.
What is the current fuel pressure at the throttle body itself? Knowing the fuel pressure at the tanks is useful, but it doesn't help identify all the possible restrictions in the fuel system. Replace the fuel filter just forward of the tanks (if you used that part of the fuel system from the 95).
Changing the fuel pump is worth a shot, but unless the TBI is experiencing lean mixtures all of the time, it might not be the fuel pressure. 95 was a change over year, so your TBI may still use 14 psi, and is more likely to use the older system if you got the motor out of a 3/4 ton 95 vehicle.