I cant figure it out, G.M. experts HELP!!!!!!?

I own a 1991 Caprice with a 5.0 engine the car has been immaculately cared for and has only 65000 miles on it. I have a problem with a ignition cutoff (RANDOM AND UNDER LOAD ONLY) the car starts good even in extremely cold weather and runs smooth that is until it reaches closed loop operation. when the car reaches full opp. temp and I put the car under load IE starting off from a stop/accelerating up hill the entire ignition cuts in and out . so far to fix the problem I have replaced the fuel pump,all filters,ignition module (4 times) the coil,the cap %26amp; rotor,all spark plug wires %26amp; plugs,the whole distributer,and the main P.C.M., the T.P.S.,MAP sensor , the ignition switch and all wiring harnesses from the collom to the ignition. no trouble codes show up on scan,all grounds are good, and yet the trouble persists! The car doesnt miss a beat when its cold it runs like a race horse but when its warmed up it runs like a FORD. Someone out there HELP!!!!!!

I cant figure it out, G.M. experts HELP!!!!!!?
You could put a few grand into it but that wont make it as good as a Ford. That's what you get for buying a G.M...Get a FORD.
Reply:Bitburger and Jeff S had the best answers. After the slam on the Fords, I hardly feel qualified to answer. You might have some do a diagnostic on your distributor. Sometimes they break down. It is a simple test but might be better to leave to a mechanic.
Reply:sdound like your cataletic converter is clogging up when enging gets up to temp
Reply:Sure sounds like the ignition is intermittently dropping out which means one of the sensors, ignition components or computer is bad so that the computer doesn't produce the correct ignition triggers and controls as it should. Is there a crank sensor? If so, maybe its signal to the computer is dropping out. Maybe a good scanner could monitor the ignition conditions as you drive the car. Make sure the battery is good and that the DC voltage to or from the ignition system isn't intermittent. For example, what if your ignition switch was intermittent? You could wire an older analog volt ohm meter to the 12 Volt ignition feed voltage point and have a friend watch to see if the needle pointer on the voltmeter is holding steady as you drive the car. Also, if you had a tachometer on the car, you'd see it's pointer dropping down as the problem occurred. That's because the tachometer is hooked directly to the ignition system output pulses. Don't forget that "new" components are not necessarily "good" components!
Reply:I'm sure there will be tons of WAGS on this, but mine is maybe the EGR valve is sticking open when it gets warm. It might only have 65k miles, but it is 16 years old.
Reply:Bitburger probably hit it. Now, you say your ignition cuts out....why then have you replaced the fuel pump? Do you know whether this is an ignition problem or a fuel problem? My advice to you is to get a can of starting fluid and try to feed the engine after it warms up. If it runs well, then you have a fuel problem. If it still runs poorly, then you have an ignition problem. I would say that it has something to do with your fuel:air mixture. This is a 1991 with a 305. The vaccum lines are probably dry-rotted as well as the intake being gummed up. Usually the EGR port. It's probably got so much carbon in the EGR valve that it has stuck open. Isolate your problem before you start replacing parts. It's a waist of money. Just like all of that money you probably paid for your ASE certification. Listen to what the old mechanics teach and it will be more valuable than any certification. Good luck.
Reply:After changing all the filters and ignition parts... I would assume that is would be ECM (computer) or the wire to the ECM. If it runs great an a cold day, I would guess the heat is just expanding thing enough so the wires are not making proper contact near the ECM. Also if it is under load, then the frame is might be moving just enough to cause this as well. Hope you find the problem, best of luck in the new year.