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).

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. If my guess is
right, the latter would indicate that whatever was clogging the injector
passed through. If the temps are still shifted, I'd have my mechanic check
the #1 injector.

BTW, this doesn't sound like an instrumentation problem since it's unlikely
that both the EGT and CHT probes and/or receiving units would go bad at the
same time.

--
-Elliott Drucker