Over Heating
As a last resort after checking every other conceivable thing that cause a car to overheat, you can buy a kit to check if you have a blown headgasket. The kit costs about $70. It tests for hydrocarbons that can only get into your coolant if you have a blown headgasket.
You can buy pills (from your chevy dealer) that will seal most head gaskets if blown (around $20). If they are good enough to use on Caddies (that's what GM does) then should work on your car if it's not boosted or running very high compression.
You can also rent a pressure tester from Autozone to test for a slow leak somewhere in the cooling sytem.
IMO the cooling system in these cars is borderline when running the A/C in regions of the US where the temps are low 90's + in summertime.
Are you sure that both fans are coming on? Have you edited the pcm to have the fans come on at lower temps? Not much use to install a lower degree thermostat and then not make an adjustment so the fans come on earlier.
I assume both fans are coming on and not a blown fuse?
Lastly, make sure you connected the two hoses at the passenger side radiator. One hose comes from the steam vent line (mentioned earlier) and goes from the steam vent line into the radiator. The other goes from the radiator pressure cap opening vent and flows into the overflow tank (to vent overflow expansion if the radiator cap opens when overheating).
Cross these hoses and I guarantee that you car will overheat when idling or after a hard pull (especially with the AC on). A shop criss-crossed mine by mistake. Took me awhile to discover the error.



