I had the exact same problem with my DD 280 TM It needed lots of trim correction, it also did not turn very well. Forget replacing the prop and replace the motor with the ips geardrive, I think the gearing is the S1. As soon as I did this it flew great with no trim correction.

Yes I did try right trust to correct the trim problem, I beleave that the DD motor is no good for the TM the plane has too much drag. The bigger prop and geardrive gives the plane more thrust.

Rob