If you have a Hitec servo programmer, you can measure the Rxer's output resolution and even see if it is stable and correct.

Also, the servo programmer's output in Manually Test Servo mode can substitute for the RXer by inputting the desired signals to the ECU. Just measure the Rxer's outputs at the various throttle and trim conditions. Then use just the programmer to input those signal levels. This allows you to totally eliminate rule out any problem with the Txer and Rxer.

The Servo Programmer can also be put on the ECU end of the harness to test the Rxer output and harness.