I have fixed my problem.
If anyone else comes across this, the issue stems from the Special input mode. In Special input you can use negative inputs on the engine to perform neutral steering. If you put negative inputs here for reversing the clutch on the vehicle will think that it is still moving forwards and will disengage the clutch to prevent stalling.
The other issue when moving forwards I have not completely fixed, but have made the symptom go away by increasing the Damping on the vehicles wheels.