Locking rear in 2001 GMC

Anyone here know what's in there and how it goes about locking it up?

Had that same type rear end in an earlier model GMC, but my problem was after many highway miles the rear would be locked up like a spool and would be hard to steer and chirp the rear tires on turns.

I changed the fluid and made sure it had the additive for "posi" units and had no more problems. You can also buy the posi additive (anti-foaming agent) by itself and add to your existing fluid. I suppose it is possible for the additives properties to be spent and need replenishing.

My experience with the GM locking rear end is that it is a good unit. I've had them in the last several trucks I've had and they've been reliable and work very very good. I wouldn't make any drastic moves before just trying the fluid change.

P.S. I don't drive my truck much--especially with gas prices as they are now. I got it in November 2000 and currently it has about 17,000 miles on it. I wanted an old truck for truck stuff and in 1999 I bought a 1977 F100 only to find it was a money pit mostly because someone had tinkered with it trying to make it a hot rod. So I sold it and purchased this one new and intend to keep it until the wheels fall off for whatever I need to haul or tow. This way I will know everything that has happened to it during it's life and it will have been cared for. Only down side is It's harder to pitch bricks into it--course I don't really do that even with the old F100 I remember telling my father just because it was old didn't mean it needed to be beat up any worse as he threw something up against the side of the bed.

While I don't miss the hot summer in the F100 without A/C, I do strangely kind of miss the 3 in a tree trans and that rough old monster look and feel. I had quite a few guys ask me in parking lots, "Dude, what year is that truck?" Heck even one lady at the office told me when she saw me get out of that truck her whole image of me changed--though I don't think it was for the better. ;) Still I used her comment to convince some of my coworkers who were teasing me that it was a chick magnet.