I just spoke with Hitec.
They believe the problem may be related to compatibility between Hitec and some Airtronics receivers.

It seems some Airtronics receivers are tuned to the "low" end of a spectrum. The Hitec as well as Futaba,etc are tuned more to the "high" end.

All three of my problems were with Airtronics RXs.

He sugessted I send the TX in with one RX...they will check it out and retune the Hitec TX if needed.

I'll let you know the results in a couple weeks.