i have your exact setup and with my ptp at 1-3/4 to 2" i get 64mph at 5800 rpms. that motor is a 6000 rpm motor, so not sure why it tells you that. First i've ever heard that.
I put a 26 pitch on it and the holeshot was horrible and got 63mph at 5300.

I do have a extra battery for the 36v TM system and 1 power pole for added weight.

Sounds like you need to raise your motor. Just raise it a half inch each time you go and see what happens.

Cup to the prop will help too.