On my 98 Suburban 2500/454 the rear end intermittently seems locked. Noted when turning particularly left turns. Dealer has looked at several times. Fluid changed which seems to help, but still occurs.
Is this when the truck is in 4wd?,does your truck have the optional locking differential? You can look on the build sheet,it should be in the glove box.It will say G80 if it does,there will be about 50-60 3 letter codes in there find the G's and if tis there ,you'll see it.Your spider gears may be damaged,or the locker's spool springs may be to weak,ir the wights may be hung up,forcing the locker to come in early or not disengange at all.
There is a Gm additive for LSD and lockers,I have never needed to use it on the G80'ssince they are either engaged or disengaged,but its worth a try.Your dealer may have already done this.I think the spring/weights of the governor assy maybe be damaged or the springs may have broken or lost tension,it sounds if the locker is engaging during small differences in RPM,which its not supposed to.If you have a drivetrain specialty shop around it may be worth your 1hr's labor charge to have them look at it.I know I could figure it out,I may have to pull the cover a few times,but a good shop should be able to find the problem.When I played with my locker with the cover off I could spin one side and once got the axle going what think was about 10 mph,the governor was spinning so fast it engaged,I watched it happen with the cover off.There must be a testing procedure in the factory service manual on how to test the unit and spec for the engagement speed,this is where I would look. Good luck John
The dealer seemed pretty cluless. I think they just put the regular posi additive in which according to the book is not necessary in lockers. Is the locker mechanism easy to get to and something I could fix w/ reasonable mechanic skills.
I had the same problem with my 93 2500. In 2wd when I turned a corner sharp, it would be locked, and leave a black patch on the road. I had a mechanic look at it and it turned out the clutches in the rear end had broken and small pieces were floating around in the pumpkin wrecking spider gear teeth etc. It ended up being a trip to the wreckers for a used diff from a 98.