I have a 2001 GMC Sierra c3 AWD truck, problem I am having is after I have drove the truck for some time and things warm up, when I make a tight turn the rear chatters. I have changed the Gov-Lock out for a Eaton posi and checked the rest of the rear out and everything looks ok, I also have used all GM fluids in it including fiction additive. I have been told that it could be the front diff causing this because it is a AWD truck and if theirs a problem up front it will affect the rear?

 

So I changed out the front diff for a new 1 and same problem, after driving for time to get things hot the rear still charters while making a tight turn, only thing I can think off is the transfer case?

 

A tight turn is only going to affect your rear diff, not the transfer case.

When turning tightly your outside rear tire turns faster than your inner tire.

The Eaton posi uses clutch packs. My bet is that your Eaton is fine and you're hearing the eaton slipping properly to accommodate the tight turn at low speed since by design you don't want it locking then! My 2004 STi had a clutch pack style rear diff and would chatter at times on tight turns.

My guess is you're OK, but lets see what others say.