[stock4174]

Years ago my low mileage 92 c3500 did the same thing. I replaced every part you did plus the cold start injector, tps sensor and even the ecm. I finally replaces the 10 dollar coolant temperature sensor located by the thermostat housing on the intake and that fixed it. There is another sensor on the drivers side head but I believe it's for the temp gauge. I spent a couple hundred dollars throwing new parts at it. I unhooked the battery to reset everything and finally got the "check engine" light to come on. I used a scan tool but don't remember the code. This might not help but you are not the only person that has had this problem.