To check to see if it was the Tx, I repaired a plane that flys the same packs and took it up today with no problems, so I'm ruling out the TX. Thanks for your time, Bax.
ORIGINAL: Bax
It's hard to say what the problem could be.
I know.[
] A lot of swapping of parts and rearranging things and I was trying to see what the likelihood of it being the part I only have one of (the Tx).
The cutting out is a new behaviour for the plane. I am quite sure it's not the packs--some of them are quite new. If it was a LVC problem, I would expect it to happen more as the battery was run down and at higher throttle rates, but time or throttle are not factors of when or how often it cuts out.
The servo in the throttle position is great idea. I'm going to try that.
Thanks again, Bax.