Z-Axis Being Wierd

So, when I move the bed in maintenance mode everything operates as it should. When I try to run a print or auto calibrate and the machine thinks it is moving the bed up to the nozzle it is actually moving down very slowly. At first I thought there was some slippage in the nut or something. But no, the z rod is actually turning counter clockwise very slowly. I reverted the firmware back to 1.3.0. No joy. Reloaded 1.3.1 from a new download. Still no joy. Anybody have any ideas?