Ok - I'd suggest that you post two threads, one in the Gunner Forum and one in the RLC Forum. That way you'll avoid sparking a truck war over whether IMMLC is better than MMLC or Gunner Log is better than Log Gunner (if those trades exist). Good luck!
Chris, I am not too aware of how the Gunners employ their drivers but as has been mentioned they generally use IMMLC (the bigger and more mobile DROPS).
If you were to join as an RLC Driver you would get the opportunity to drive IMMLCs, MMLC (the smaller DROPS), fuel tankers and the whole range of general service vehicles. Depending on what unit you went to or what operational tour they were deploying on you could also end up driving a range of wheeled armoured vehicles and/or WMIKs.