Glen,
I am asumming this is a three wheel truck if so then I might be able to help
the code 99 referrs to service your truck is now due for a service, Your truck may be restricted to half speed or less.Code 250R is probably refering to the right hand drive motor.
Brake not coming of brake coil open circuit,
Mechanical failure of one or both traction motors.
You could use the dash display dianostics to check drive motor encoders.
Check for 12volts at wires 83 and 84
wires 81- 82 go to thermal unit on motor
There may be a six pin connector on motor measure resistance on any combination of wires resistance should be at lest 1 meg.

I hope this is helpful.

Titus