Prentice, The MPW has speed settings adjustable through the controller using the curtis handset. If the jacks runs fine then the speed drops something is either dragging like the brake or the system is getting hot or possible gear issue in the drive unit if the oil is low. Have not had a problem with the drive unit as long as the oil is maintained. When the battery voltage drops the lift goes into lift lockout but should still travel at normal speed so it can be brought to a charger. You may also want to check around the drive tire and gear case to ensure no build up or material jammed in. If you need additional info let me know.