One little mistake that can cause your problem, is having your ailerons deflected, rather than in-trail. If they are both deflected downward, that will indeed have the same effect as incorrect incidence (too much positive incidence).

If your ailerons are perfectly in-trail, try reflexing the ailerons upward a little & see if the problem goes away.

The trim changes could be caused by push-rod expansion & contraction, but it shouldn't be especially noticeable -- unless you have the throws maxed.