[JohnnieB]

When measuring between the M- and B+ terminals on the controller in a series drive cart, the voltage ought to at or about Zero when the pedal is just pushed far enough for the solenoid to click and then should increase to the Full battery pack voltage (at the time), less about 0.5V for every 100A of current flowing through controller.

If you are monitoring the voltage between M- and B+ while driving the cart, the battery pack voltage may very well have dropped from 38.0V to 35.1V while under load.

If you have two voltmeters connect one between the controllers B- and B+ terminal and the other between M- and B+ terminal. Those two readings should be nearly the same when traveling at max speed with pedal on floor.

If you only have one voltmeter, measure between M- and B+ and then measure between B- and B+ while traveling over same stretch of road.

If the voltage readings aren't almost the same (within 0.5V or so when traveling at max speed on level ground), than the ITS may be out of adjustment or bad. or the controller is sick.