Here's a few thoughts of mine.

First, take a look at where the elevator is trimmed for level flight. This can tell you in general if something is wrong.

The fact that you can't trim for full throttle and the plane wants to climb indicates you have something in the incidence-thrust line area incorrect. I would go over the plane with an incidence meter and compare wing, stab and engine incidences.

A lot of Extra-CAP planes need expo on elevator.

Reflexing the ailerons up an eighth (1/8) inch helps on the landing of the Sig CAP. It's not quite as large, 73", I think, but it's in the ball park so you might want to try this.

Another thing I have used is landing spoilers. You set flaperon wing type, then mix throttle and flaps, having the flaps go up 1/2-1 inch at idle. I set the offset so they retract at half throttle so if I go around, they aren't still up. I arm them in the landing pattern.

Finally, adding a 6-8inch long stall strip at the wing root can cure a lot of tip stalling. Use something like 1/4 -3/8 triangle. You can tape it to the leading edge for a test. This has worked well on .40-.46 sized planes.