For Mud Bashing you need a certain amount of Torque, and then you are wanting a high turn rate to "Paddlesteam" your way through nasty muck.
I would fear having an Electric truck in Mud.
I agree that any truck would want a servo upgrade. There is a servo bash plate available for the Maxx and yeah it would be recomended. for Mud Bashing I'd recomend some plastic and/or Leak sealant to realy protect the servo because of it's location