91 beretta Runs on 5 cylinders!!!

I have an 89 chevy cavalier z-24 with a 91 beretta 3.1 under the hood. About 6 months ago it started running rough and would stall when the engine warmed up, and wouldn't start again until it cooled down. We changed and or checked the coils, changed plugs and wires, egr, injectors, fuel pump, intake gasket, plenum gasket, tps, checked for vacuum leaks, and replaced the exhaust system. CLUELESS. Now it will run with no problems for about five to ten minutes usually, and i'll lose a cylinder. Sometimes it will run without any problems for hours, but when i start it back up, i lose a cylinder. Any Ideas???

Thanx
Tony Osterhoudt

are you losing the same cylinder every time? the first step would be to see if you're losing fuel or spark. when it dies, pull the plug of the dead cylinder. if it is wet, you are losing spark. if it's dry, you may be losing fuel.

in my experience, a car that dies when hot either has a fuel pump failing, or a coil pack failing.