Only two posibilities.

1) If the power of the pump (Pw=xx) don't change while the engine accelerates, then clearly a pump/plumbing problem.
2) If it raise, the its the TX that is asking for more RPM. Had exactly the same issue yesterday with a M90 and a MPX4000 TX. Engine had unstable idle. One click less of trim and steady idle. Relearned the TX and all OK again.

Gaspar