So the problem I’m facing is the Y axis. ChatGPT says it’s backwards but if I invert it the problems are worse. Anyway with a laptop connected and using minicom/picocom to tell the printer to jog to say G0 Y10 the bed moves forward (towards me) if I issue G0 Y-10 it moves back (away from me) is that the correct direction?
I had klipper on this printer before but kept running into layer shifting so I went back to Marlin.
Your Y is right, ChatGPT is wrong. Y0 is the front edge of the bed under the nozzle, so homing sends the bed away from you, and G0 Y10 brings the bed toward you. That is the normal direction on any bed slinger. Inverting it would be the mistake.
So the Y axis is not your problem. What is the actual symptom you are seeing: prints mirrored, crashes at the back, layer shifts still? With a 400x400 extender the usual suspects are the Y belt tension and the Y stepper current, both of which also explain the layer shifting you had on Klipper, since that would not have gone away with the firmware.