[SoCal LS-L]

Originally Posted by redlightningsvx

It overheated slightly when slowing down to about 40 or less but going anything above that it was fine. And if it overheated when slowing down I just went faster and the temp gauge went down. The coolant is new as I replaced it when I replaced the thermostat the first time.

It would really seem to be a cooling efficiency issue, as the car needs a lot of airflow to keep the coolant from getting too hot. The coolant may be new, but have you removed the radiator and turned it upside down, feeding water into the lower hose port and flushing it through the radiator? This would hopefully clean out your internal passages by flowing water in the opposite direction than normal when its on the car.... the passages are really small and even a little gunk or sediment can affect cooling efficiency a lot.

The only other thing I can think of would be a restriction somewhere in the block or hoses, but thats most unlikely, and you have replaced the thermostat twice also. So if you havent yet, id try pulling the radiator and flushing the heck out of it.... that CLR Cleaner (Calcium,lime,rust) would also help get rid of deposits, just make sure you flush it completely out of the radiator.