1994 gmc k1500 sometimes dies when idling and sometimes wont die until you put into gear no codes in computer but can get engine light to flash once then twice only thing I can get it to do have replaced fuel pump tps iac map sensor cannot find vaccume leak nor can I hear one

The code is a 12, it is start of test it should be there, the most common thing on the GMC or any GM product was an idle control valve or motor which ever you want to call it, but you have already tried that. so the next most common thing was the pick up assembly inside the distributor the magnets get week an when the RPM gets slow the pick up is unable to read the magnetic pulse and when this happens the on board computer system thinks the engine stalled so it shuts off the injectors and then the engine stalls for real.

try replacing the distributor with a re-built one, the problem is so common that most auto parts stores keep them in stock.

I would recommend trying to clean the throttle body and maf. It really sounds like a IAC problem, but you replaced that. Only other thing it could be is a vacuum leak, but you said you dont hear much of that either. Try cleaning the throttle body and maf, also check the airfilter and make sure its nice and clean.