I had a issue with the thermostat sticking open at the last year. Engine ran in the 110-120 degree range with the thermostat open all the time while running hard. I could turn 5000RPM on almost any day with it running like that. Replaced the thermostat and put the recommended 160 degree thermostat in and lost 300 RPMs. Engine runs about 170-175 with the 160 thermostat in place. Pull the thermostat out and I get the RPM's back. The ECM has been reprogrammed, MSD ignition, after market flame arrestor, other than that its stock. All tuning is the same as last year. Fuel pressure is approx. 42 psi. Any ideas? Is it running too rich for the higher engine temp or does it run better at the cold temperature because it is running on the cold temp. enrichment indicating that it is not getting enough gas on the top end?

Brett