[2000CAYukon]

First thing that I would look at is the Engine Coolant Temp sensor in the intake manifold near the tstat housing. You can use a scan tool to see what temp it is reporting to the ECM or you can use a volt-ohm meter to read the resistance when the engine is cold and hot. High reistance is cold and low resistance is hot. The resistance table is probably posted somewhere or post the results and someone can tell you what the values are.

If you unhook the ECT sensor, and run a jumper wire between the two wires in the harness, this will tell the ECM that the engine is running warm and if the problem goes away, the ECT sensor is bad.

Another thing could be a clogged exhaust or cat. As the engine gets hot, the exhaust blocks and you can get a backfire or popping thru the TBI.

Also check the heat riser in the air cleaner housing. As the exhaust temp rises, the heat riser should close so that cold air enters the TBI. As they get old, the valve does not close enough and hot air enters the TBI. I doubt the heat riser is your issue but can hurt to check it.

//2000CAYukon