I have a 04 trailblazer with the 4.2. It overheats in stop and go traffic unless the heat is on. And at idle. It will stall at traffic lights if not in neutral. Doesn’t have milky oil or any kind of smoke from the exhaust. Does smell like it’s running rich. I don’t smell antifreeze. And I tested the coolant system for exhaust gases and it didn’t register any. No bubbling in radiator either. When it 1st started happening I noticed the fan clutch wasn’t kicking on and the water pump sounded awful so I replaced those. And the thermostat since I didn’t want to fight to replace it later. Fan clutch kicks on fine. I did take some coil cleaner to the radiator and it helped some but still overheats. Person before me did put universal in and I’m pretty sure it calls for dexcool. I know you can’t mix those but my truck was flushed a couple time then changed to universal and it’s fine. I don’t drive the blazer since I have my truck and a car but I’d still like to keep. The 4wd has came in handy a couple times.