I ran just this code and the servo doesn't move or jitter, but my pwm meter still shows pulse intermittently going to 0000.
But a really strange thing happens. When I put my hand between these wires the servos start turning in crazy directions: full rotation of some, sharp movements of others. And yet there is no code commanding them to move, though they are still wired. I wish I could somehow show you a video of it.
The servos will randomly move with floating input lines, which is what you have with the arduino pin in the default input mode.
More important is that you are still getting the occasional lack of pulse from the receiver. What happens if you put a small signal diode between the receiver and arduino, so that the receiver can only pull the input LOW, and the pullup to 5V cannot affect the receiver? Edit - do not think that will work in this situation
I'm trying to run the code on an ESP23 to see if that works, but I can't get the CP210x drivers to download and work.
Is there anyone in the southern California area that I can visit/hire to:
Thanks!
Hi, @ovalracer
This might be a time to start soldering connections into your final project.
It sounds like loose or bad fitting jumpers, particularly power supply jumpers.
Tom... 
I like your test rig - looks very handy. However, I suggest that for now, you see if you can wire up your Mega with minimum components and keep it well away from your other electronics.
I'd be happy to help in person, but I'm in NJ, so it would be a bit of a hike 
I believe the OP was running the code I posted, which left the servo drive pins in input mode. That code was meant to test if the pull-up to 5 volts on the input line was somehow causing the receiver to malfunction.
