You can go to full time from part time. Usually it is for a temporary time frame and for a special reason (a hardship of some sort). Check with your manager or HR to be sure. I have seen it done, but very rarely. As for your pay I have also seen that cut due to holding a part time position. Again check with your manager or HR.
Being in a driving position, you are valuable because we cannot just pull someone off the street to fill a driving position. Where as with an unloader/loader, they all come off the street. You may encounter some resistance in trying to go part time.