An important question was asked but not responded to.

What size Prop are you using?

I use a TT GP42 on a 6.5 pound trainer and it was a dog on the recommended 10x6. An 11x4 was ok, but an 11x5 is a great prop for this engine and plane and reallly woke up the performance.

Also, I'd second the advice to by an Aviastar .53 for your plane.

Jack