You should make every attempt to duplicate these problems on the ground in a flight stand. At what range were these problems ? You can put the TX in range test mode and back off a few hundred feet to simulate extreme range. What were the recorded max/min RX telemetry voltages ? Test with the engine running and not. Jerk the sticks around like you were doing 3D.
Are all of you guys getting your extension cables from the same aftermarket place ? A guy at GMA who manufactures planes was having these same kinds of problems for months. All manner or things were accused including chrome monocote flapping in the wind. The end result was aftermarket extensions made by illegal orphans in a basement somewhere.
Lastly there is not a temperature range specified for these receivers. Do you have open canisters in the fuselage, a big clear canopy, and no air vents. This caused problems with the original 6014FS receivers. I put two in a pyrex bowl in my oven and heated them up to 140F. Mine worked fine.
Good luck with this problem.