"PaulH" wrote
Were you running lean, rich, peak? Fuel injected?

Yes it is Fuel injected (I did mention that it was an IO550).
I was running 14.8gph at WOT (which is LOP).
OAT was 52F, OilT was 188F, TAS was 160Kts, Alt was 12000ft.

I'm no expert, but the symptoms seem compatible with a partially
obstructed fuel injector. This would cause the mixture in the affected
cylinder to be leaned (ergo higher EGT if you are running ROP) and power
to decrease (ergo reduction in CHT).
-Elliott Drucker

Yes I agree that would be consistent. Although aren't there many
other explanations for the same phenomina?

From your post I can't tell if the temps stayed at their altered values
on subsequent flights or reverted to the "before t = 0" norm.

Yes I forgot to mention - on subsequent flights everything reverted
to normal.

Thanks for your inputs

~Paul