1994 gmc sierra ext.cab4x4 takes forever to start stalls immediately when it does start chkd. fuel system Is Fine changed distributor, cap rotor wires and plugs map sensor,computor TPS ,

COULD BE A WEAK FUEL PUMP

plastic distributor ? wrong screws in rotor? timing?

try taking egr valve off and cleaning that and also check the o2 sensor . if not that maybe a hotter plug ?

The distributor gear. It wears down and causes rough idling to no start. Pull the distributor, look where the rotor button is pointing as it needs to go in the exact same position. you can get just the gear and replace it. it is held in by a drive pin. Push it out and swap gears and reuse the drive pin. hammer it in.

check fuel presure

yes i have an idea. you may have a bad idle control sensor. you have the symptoms of it. so far as you've posted. the sensor cost's about $20.00 ONLY 2 SCREWS to replace and any parts store that you purchase it from can tell you where it's located on your engine.usually on top of engine,silver canister type w/one plug in[electrical] also when replacing,disconnect the positive cable on your battery, this allows the computer to adapt the new component to the system. if there is anything else i can assist you with,please repost your question to fixya.com there are plenty of nice people out there that will be happy to [assist] you. thank you for choosing fixya.com

i have a 06 sierra that done the same thing and it was the distributer gear stripped

Check the fuel pressure at the shredder valve, the valve is along the fuel line by the distributor cap and there should be 62 to 65 PSI. Anything different will give you a not start or run, The other things too that would stall the engine would be a faulty oil pressure sending unit, anything less then 4 psi will shut the engine down and a faulty ignition module will do this too. Once the module heats up it fails, it's common for moisture to develop in the distributor and corrosion occurs to the wires leading to the module. Start with the simple and check the fuel pressure and then to the gauges, like the oil and then the ignition module. Good luck and keep me posted, be glad to help you resolve the issues to your GMC.

Check if any spark or fuel.

its your fuel pressure regulator!!!!!!!
change that!!!!!!