More thoughts -

Your prop just might be indexed correctly but differently than the ones
I'm recalling. That seems to be a snake oil thing with different
aircraft.

Another lo-cost check would be to do an oil analysis on a sample. I
know of an engine that would get really stiff when warm that had a bad
cam lobe & misc bearing contamination. It would free up on cooldown.

I contend the equal cylinder-feel-on-hand-prop test is an effective way
to check out the upper end of an engine, although it would not uncover
any lower end mayhem. An oil analysis is the cheapest way to check or
track the lower end. Be sure to take the sample correctly though.