You may want to balance your plane. If it is nose heavy that will require higher landing speeds and cause your plane to stall at a slightly increased speed.

OS Recomends the break in prop to be 11x7. For flying sport aircraft you should use: 12x6, 12x7, 12x8, 13x6, or 13x7. Only if you have a Tuned Pipe use: 12x9, 12x10, 12x11.

That being said you may want to check you low end idle RPM. Does it pull your plane while its in the ground? Or can you idle in place? Also use a prop with alittle less bite such as a 12x6 or 12x7.