Hello Barney,
I've tried it on a truck we have in our stock, and it working all the time. Only if driving for example forward and changing the directional switch in forward the truck still drives forward you can only change by pushing backwards direction. Is this problem only happening when the steering wheel is at 90°? Can you tell me if the steering angle on the display is pointing correctly and if isn't giving any error messages. Could be that the switch for drive position detector is fault or well adjusted.
Kind regards