When the current knob is then set to full, the
voltage returns to 13V and the current goes to 4 amps (should be 35A).

No, it should be 13V / 3 ohms = 4.3A.

Sounds like he needs a 0.37 ohm resistor to allow a 35A current at 13V. Better
make it a 500w resistor or better to handle that kind of current.

I agree, it sounds like the P.S. is working properly.

Alan Harriman