It's not normal. Do you know where the controller is?
If so, Have you looked at it when the problem occurs to see if there's any errors?
Have all the electrical connections been remade from the battery to the motors?
If not, I suggest that be done, especially between the controller and motors.
Does the lagging happen randomly, or only when leveled, or only when not leveled, etc.?
How often does it happen? (every other time, Once in a while, randomly)
Is there any unusual noise when it is happening?
Salem 29RKSS Pushing a 2500 Mega-Cab CTD!
Gotta go campin!