So I go to Advance Auto Parts to get everything I need to flush and fill the radiator as well as change out the thermostat while it was empty. After draining the coolant I get the old thermostat off and try to put the new one on and it wont fit. Anybody else have this problem? I jumped on my motorcycle while I still had it off to go see if Advance had an optional one that may fit and they said this was the only one they had listed for this truck. I then went to Autozone and O'Reilly's and theirs was almost exactly like the one from Advance. Can anybody help? If you found one that fits where did you get it from? By the way its for a 99 Silverado 1500 w/ 5.3L.