Im gonna say thats a real possibility now. I had a similar issue with my front diff.... had to change the fluid twice to completely resolve the issue I was having (binding popping sound in front).

Get enough fluid and mopar friction modifier for two complete changes. It'll probably get better a few days after the first change... then a week or so of driving change it again and you should be good. It takes some time for the fresh fluid & additives to work its way into the clutches; so dont be discouraged if theres not an immediate improvement.