1998 stalling problems

I have a 98 cavalier with a 2.2 with a 5 speed. When I run the a/c, the car tends to stall out. It started this last year and has gotten worse this year. It usually only does it in town or short trips, rarely out on the highway. I can turn the a/c off and shut the car off and start it right back up and it will usually run fine with the a/c on for awhile. I have replace fuel pump, fuel filter, plugs and wires. Anybody have any ideas where to look next?