Pot: 2.5vdc in neutral.
I would have expected a code 80 if the pot had an issue. Regardless swoop may be onto something, let us know.

check the control handle travel pot also...

on the ray/cat trucks they did this and generally the pot was going bad and caused the truck to move erratically, anything from creeping when the handle was in neutral to erratic travel movement and even as you said, actually moving in the wrong direction when activated.
Usually a relearn of the control handle fixed it but ultimately in the end the pot had to be replaced and calibrated/learned.

and as you said this also can cause it to be very difficult to get the truck into maint mode to do the learn, it can be done but you will have to keep moving the handle and holding it in different positions till it likes what it sees to allow you to enter maint mode. Using a vom and monitoring the signal might be helpful in achieving the desired voltage range for neutral till you get into the maint menu.

Use oem parts here.
I tried a tvh sensor once, the optical eyes are set too high and too close together. Truck acting as you describe. Raymond sensor - all good.

You can probe the connector with a voltmeter. Pin 3 is +12 supply and 1 and 2 are sensor feedback, grab b- wherever. Take the disc off and put metal over the eye to close the switch and you can see if it's opening and closing. Typically open has 0-3 volts and closed 10-12. You may have a dead eye.
Good luck.

okay thanks for the reply i will check that out.

Sounds like a speed sensor issue. It is located on top of the drive motor and reads speed and direction from the segmented disc. the gap should be less than 1/8 inch. Make sure that disc is not bent.