Thanks for reply! Code 28 is just exhibited at full speed. I will see the truck tomorrow and I will tell you. thanks again

If I read correctly this code occurs at speed. You need to check your encoder as noted above. Also check the shaft on top of the brake that the encoder mounts to - make sure that it is tight. More likely though, you either have a mechanical brake issue, the brake is worn out, or your brake cylinder is leaking. This code with travel more signifies that you have a stopping problem than an encoder problem.
I would recoment plugging to stop vs taking your foot off of the deadman pedal.

That code shows excessive acceleration from the drive motor. If it happens during selftest, check your brakes. The drive motor gets pulsed during selftest and if the brakes are weak you will get this code. Also check the motor encoder belt and pulleys at the top of the drive motor. If worn, change em.