I have noticed with pe models 4000 and 4500 that if ur first reply doesnt solve your problem check your raise lower solenoid as strange as that sounds it is a common problem with our fleet.

One of the direction micro switches in the handle are out of adjustment or the traction pot is pad. The specific switch must close before the trac pot reads 1.5 volts. In simpler terms the trac pot should read about 0 volts at rest. And go up to approx 12 volts positive in one direction and up to 12 volts negative in the other direction. Before the voltage reaches 1.5volts the microswitch must close. this is ofcourse ASSuming the micro switches are good and the trac pot is free of opens or shorts. Hope it helps.