Albatross- There is a fine line on the 110 between perfect on the high and too lean. If you are a little rich on the high it can cause the upper mid range stumble.

If you let your engine idle for 20 or so seconds (on the ground while restrained) and goose it does it stumble? If it does not stumble while motion less on the ground, you will have to look at other causes.

Wish I could get my temps that low, but I haven't finished my baffling work yet. By the way how hard were you pushing it in that chart above?