That is usually a sign of a slight "kink" somewhere in the cable. Most likely in the cabin.

The cable resides just behind the accelerator pedal. Make sure it has some slack to it and there are no unusual bends. A damaged cable could also do what you describe, but typically, the needle would vibrate at ALL speeds...

__________________
2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car