One thing that you might want to try is to slightly raise up both ailerons( i.e. move them equally together about a 1/32 of an inch up) this will slightly decrease lift and may help with this problem. There was a post from another member who said that if your plane tends to need a lot of down elevator when inverted, then try raising both ailerons......especially if you notice that when you fly normally, and hit the throttle if the plane "balloons" upward that is it starts to climb, than turn the aileron adjustments equally to raise up the ailerons, try a tiny amount and see how it goes.