I have a 1992 chevy CK 1500 truck that when in gear and at a stop light or stop sign with my foot on the brake the rpms fluctuate and drop and then eventually it will stall.. I did a tune up on it recently... I put new plugs and wires distributer cap and rotor in and I am really getting frustrated because I have to double foot while driving in the city and most of the time to keep the rpms up.. any ideas what my problem could be?

Sounds like you've covered a lot so far! But what you've done is all secondary ignition. If they were at fault, you'd probably feel a noticeable misfire.

Without having the truck in front of me, I'm just going to fire off a few things : possible weak coil, sticking or clogged throttlebody (especially at idle), low fuel pressure/volume (fuel pump or fuel filter) or restricted exhaust system...

If you eliminate these things...