I'm running into the same thing with that servo on my son's EB48.3. I'm using it as his steering servo, with his 4PL radio. When I turn the controller wheel back and forth quickly (like doing a whip off a jump / maneuvering the car in the air to set up for the next turn), the servo seems like it will go back and forth several times at the same speed, then all of a sudden it's like it hit a turbo boost or something.

I tried lowering steering and return speed, expo, even changed the receiver, but nothing worked. I called Futaba, and the guy said "he'd never heard of anything like that happening".

I had to put the HI-TEC 7955TG back in there for him to race.....it's smooth as silk. I'm going to try it in my buggy with my 4PX to see if it's radio / receiver related.