Well I ran into an issue similar to your sputtering one just after I got my car. It turned out to be basically all the sensors located on the thermostat housing having bad wiring. Old wiring was cracked and really crappy. I would definatly check into that. For the guy who is having an overheating issue with a clean compression check, do u have electric or stock fan on your car? If you have the stock fan, is the shroud still on it? And if that is all there, have you tested the fan clutch to make sure it is working? A bad fan clutch will mean your not pullin enough air thru your radiator. For the one with the 14" fan and the 2 accessory fans, are they wired on a thermal switch, or are they controlled by a toggle? Are you sure your fans are in the correct orientation, Pullers? Are they pulling enough CFM thru the rad? When doing a compression test, you have to do it when the engine is hot. And if you have any fluids in the cylinder bores when you pull the plug for the compression test, then U have a blown head gasket. They needed to deck the block if you put a MHG on the car. And if they didnt then it was on you to make sure everything was done correctly before assembly. Always verify the work that has been done, before the engine is assembled. You could also have a clogged heater core too. Make sure to back flush and burp your cooling systems to make sure everything is flowing correctly. If they didnt clean the block correctly, you could possibly have a clogged cooling journal on the block, or anywhere in the engine compartment. But I would check the heatercore, Get a length of hose and bypass the heater core for now. If that works, you may be in the market to be replacing a heater core. Just a thought. And im guessing you have also checked your waterpump too. I cant remember if you said it was replaced or not. Chances are its your cooling system clogged somewhere if your not blowing white or blue smoke. (white being coolant, blue being oil)