I had nearly the exact same issue with my '89 Chevy. Would idle fine in Park and Neutral but put it in gear with the brake pedal engaged and it would idle rough and/or die, and sitting at a red light it would die as well. At speed it ran just fine though. Also, on occassion it would die coming from highway speeds to stop for a light or stop sign. Tested the IAC, TPS, CTS, EGR and MAP, all checked out good. Replaced the fuel filter but no change.
I happened across an article (that I can't find right now) that talked about the piece of fuel hose between FP outlet and feed on the pump itself that is prone to splitting. I checked fuel pressure and it was at 8 psi. Pulled the pump and found that, indeed, this piece of hose was split. Replaced the hose, checked fuel presure and it was at 13 psi, issue solved.
Checking the fuel pressure, in my mind, is a good place to start. HTH.