How about the errors shown on Pathfinder (Linde Diagnostic Software) I understand, the disgnostics with the computer has been done by Linde service.

By the way, the fwd and rev selenoids are activated by the proper power not voltage.
You may check it with diagnostic software.
The wheels should start to rotate at circa 440/460 mA.
With the fully depressed acc pedal the value should be about 1220 mA.
The desired traction wheels speed should be ~ 200 rpm.

Generally, in my opinion, you may have problems with the traction pot. Even the calibration itself may not be enough. The pot may be anyway dead.Possible is the problem with the gear or pinion gear linked with the pot.

Still - it's all speculation. Yo can get the answers simply asking the dealer service (I understand it's Linde) for some serious computer diagnostics.