[What's_nitro?]

You said that the jittering was worse when the truck was further away, and that would suggest radio interference. The BEC output might cause interference when in such close proximity to the MM's signal wire. It is after all a switching BEC, so some RFI could be leaking into the output leads. You may even want to wrap the BEC in aluminum foil to shield everything. It's all I could come up with aside from MM settings, but that's been suggested already.