U-Force 75, lehner 5300 Problems

[RC-Monster Mike]

Welcome to the forums, Justin. :)
I would bet on the batteries. The Schulze controllers do exactly what you describe when the voltage drops too low(55 some odd % of initial voltage at plug in). Low quality batteries drop voltage in a hurry when under a load. Try another set of batteries, or even better battery connectors as Serum mentioned. It seems like low voltage based on your description.