starting/ warm idle issues

i've had this problem with my 89 for a few years now. it starts and runs fine, but developes a miss at warm idle. almost like it "loads up". on warm starts, it will turn over, start, them stumble and almost die. the vacuum gauge that I installed on my dash shows the vac start at 20, then bounce around at 15. almost every sensor is new, no trouble codes, I just put in that new engne, and replaced the fuel regulator and injectors. any ideas would help. could it be the pickup coil in the dizzy?

oh, it also stumbles/surges under very ligh acceleration, light driving in a parking lot

Did the 89s have the 5.0L? I'm not too familiar with that engine, but I'd start with the EGR system. If the EGR valve is stuck open or commanded open when it shouldn't be it will stumble at idle and light acceleration.