[BrianG]

So, two totally different systems, even motors? A radio wouldn't cause that since it sends low power signals to the ESC. At most, a faulty radio would simply not work, or send the wrong signal.

I assume you checked the usual things: How do you have the gearing? Is there any driveline binding?

The batteries could be at fault, but may be hard to tell unless you get an Eagletree in there.