Call the company.
Is the motor rpm hopping around with all the surfaces?
Or only certain surfaces ?
Check each connection by GENTLY squeezing bullets, or GENTLY pressing a connector into the receiver board.
If everything is jumpy check the crystal freq. & that the trans. has a trans. Rec, has a rec. crystal.

Call the company.
Almost forgot. NO metal pushrods into any other metal parts. NOISEY. NO push rods laying on each other.

I LIGHTLY twist the motor leads to get about 2 or 3 turns in 1 inch of length.

Rich