You describe so different power situations (double trap vs. two sitting on the hulls) that I can't imagine a few pounds more or less in the diamond could make such a huge difference. I would guess that either there is something REALLY wrong (mast not stiff enough so it bends back way too much or not enough main sheet tension) or you just didn't get into the same groove as the other boat. For checking trim, you should foot enough to get both out on the trapeze with the windward hull flying and then try to head up slowly, maintaing speed and the windward hull dry. Now by changing trim, try to improve the upwind angle you sail with respect to the other boat, maintaing more or less the same speed. It is here where the diamonds, cunnigham and all that come into play, imho.