You said the coolant temp. was lower before the 3.2 swap, and that was with an old radiator. I'd think that it is not anything in the cooling system since that was not a problem before installing the new radiator. Maybe you are running at too lean a mixture which would cause the temps to run hotter. Does it run smooth and quiet, rev, and idle just fine ? Is it noticably quicker than the 3.0 ? Are you using an MAF and/or LPM ? rather than continuing to buy various sensors without knowing for sure if one of them is at fault, maybe get a dyno reading on the a/f so you know for sure.