As an aside, you won't be flying too much precision aerobatics with rudder mixed in! Will have to switch rudder mix out before performing aerobatics, then back in for cruising/landing.

I agree with above post - sounds sus. Fly high, cut the throttle, and see how it turns on a fast glide. If better, it's obviously engine-related. If not, check all your surfaces for warps/incidences. If it IS the engine, apart from prop changes, check the sidethrust - see if it pulls up straight into a vetrtical line from level. If pulls left, maybe put in a bit more right thrust.

Good luck!

Cam