I have a 3.3 motor in a OG Slayer I bought used. I replaced the head shim and cleaned it before running it. The engine starts up good. But after running it for about 15-20 min it starts to idle high and the temps start to get out of control. I can turn it rich and the temps won't go down. I have the carb almost closed at idle but it still starts to idle high. The truck runs good, till the idle problems make the heat start to go up. The top of the piston was still sliver with very light brown near the intake ports. Any info would be helpful, thanks in advance.