Problem: loose/sloppy IRS Rear end. Solution: rebuild or replace (posi)

I have a 99 cobra with IRS and it is sloppy / loose. Whenever I shift and start to go you can hear a clunk. its not crazy but its not that nice. When I am going down the road if I let off the gas and then give it gas again sometimes you can hear it as well go clunk. So my question is should I rebuild it or replace parts to make it better or should I go with a new rear end such as posi.

I have some money but I am tight right now and will be in much better situation in about a year or so. Please advice would be greatly appreciated