i need a driver side rear door for my 2001 Jeep Grand Cherokee. What years interchange for it?

Any auto salvage yard or parts dismantler can look up compatible parts on their parts interchange, even if they don't have one available they can let you know which yards in the area do.

According to the AllPar site, the Grand Cherokee body style was the same from 1999 - 2004 so any of these years should fit your 2001. http://www.allpar.com/model/99gc.html