I test the motors on JAK blocks wired directly to a bench supply where I can measure current and voltage. If the two work in both directions with the same relative currents, I'm pretty sure the motors are not bad. Combine that with checking for any binding, and you've 99% eliminated a motor or mechanical issue for this kind of problem. Turns out that one of the motor leads was shorted to the motor case, and I suspect that took out one of the driver transistors. The reverse board drivers were running hot even in neutral, that's certainly not normal. 
A new reverse board and the engine is happy again.
I agree that if an unloaded motor is pulling anything more than a couple hundred MA, it's most likely bad.
