Irratic idle/stalls/restarts/dies

I have a 1994 pontiac sunbird with a 3.1 multi port engine. It has a new fuel pump assembly and fuel filter, the car starts just fine and drives with no hesitation or surges, when you come to a stop sign or light the idle will drop down and idle rough but will pick back upafter quickly. Although sometimes after the motor is warmed up this problem becomes more and more relevent until the car will just die and you can hear the motor grind to a stop and I mean grind like its ran out of gas or diesling on. After the car stops it will start right back up and you can rev the motor and all, but as soon as you put the car in gear it dies again, any gear but park and neutral. After about 5 or 10 minutes the car will finally stay running when you shift into gear and away you go for about 10 more miles and then the same thing happens.I have let the car just sit and run and the only thing that happens is the idle seems to fluctuate a little but not that much, but as soon as you put a load on it thats when all the problems start again. What really stumps me is how the car dies when you put it in gear but has no problem just running in park with no restrictions. I have been told its my iac control, throttle postion sensor, fuel regulator even my catalitic converter, could you please point me in the right direction.I could understand these sensors and regulators but why does the car keep dieing when it goes into gear but runs fine in park.