MJ,
Anyone who answers before you give a few more details should be taken with a grain of salt. How many years do you currently have in, is driving your only goal or would you considier friend/T management, do you have a degree or nearing it and i hate to say it, do you fall in any minority classification.
In many areas of the country you may be doing the same work only with a new title (ex..covering for call off, no show, etc .....and please YES I KNOW NO MANAGEMENT PEOPLE SHOULD EVER HANDLE PACKAGES but we will defer to reality to help MJ because we all know it happens)
If you go into P/T supervision it is very difficult to become a driver. Someone can correct me but i believe 6 union members (p/t with the seniority) must be taken before UPS can throw in 1 p/t supv or outside hire. So you will still be a fish its just that as a p/t its in a smaller pond with a smaller school.
I'll defer any other comments till you give us more details to hopefully help your decision