I'm going to ask a load of daft questions so please forgive me if you know all this
Is the RX 40MHz FM? (I am assuming the TX is 40MHz FM)
Are the Crystals FM?
Is the RX just a standard 40MHz (not HRS or PCM?)
Rather than just altering the trim have you reset the end points on the speedo? Is the speedo brushless?
Cheers,
Ian