I take it that there are no codes being thrown... like for a bad knock sensor?A higher octane fuel gives a more even burn. I use a contour zetec with stock management on the 93 octane w/o detonation or preignition. I'd pull the temp gauge sender, and test it to see if it's reading low. Make sure the coolant temps aren't actually too high. I'd recheck static and ign timing also.
