i just checked the nosram esc is rate at 6v/3amps the savox servo is rated at 6v but it has a stall current of 5000mah (5amps) now just to clarify your problem is only happening when you go from lock to lock or under load and i would hazard a guess the its glitching at that point because the amp draw is above 3amps.
what you may find if you put your exact setup in a tc with no cap you would have never had a problem because the whole steering mechanisme (including Wheels) is lighter so it would need less current to move every thing.
like i said previous its good you fixed the problem and i hope this clarifies a few things for everybody.
stu
