Brian, just as a suggestion on something you might check.
My '91 300SE started shifting a little harsher than usual last month.
Then I noticed the engine temp was running about 70-75C, about ten degrees lower than normal. The bad thermostat was replaced, the temp went to 85C, and the tranny started shifting normal again.
But, just like yours, my little engine can't handle hot weather and AC, and it always shifts harder in the summer, just trying to move that big car.

DG