How do i fix a posi rebuild and a limited slip.

4 wheel drive is unfortunately a bit of a myth as in 4 wd any two wheels with no traction will not move you any where
so if you have both rh side wheels slipping,
go no where
left front right rear ,
going no where
the wheel that was not turning was the only wheel that had traction but through the differential action the other wheel spun faster
now with limited slip diff centers , both wheels have to turn as the differential action locks up so yes you would be going some where.
posi traction is the same idea
vehicles that have limited slip diffs are Toyota and Nissan as standard with some Nissans having limited slip diffs in the front drive axle as well
now if you are doing a lot of 4wd driving in adverse conditions , you need to have locker diff centers ( available from off road shops ) as they physically lock the diff actions ( with the flick of a switch) with the result if all 4 wheels are spinning and you are not moving , your stuck but if one wheel has traction you keep moving

call the ford dealer without knowing if it is a posi,limited slip or just a plain ole corporate hard to say just have your vehicle id number ready and call and ask for parts dept at the ford garage

Technically you do not have 4 wheel drive, you have two wheel drive (possibly three-wheel drive). When you engage 4WD you direct power to the front and rear differentials. The front differential is an open style which means that only one wheel will drive, and the rear differential is likely the same type which means that you will only have two wheels driving the vehicle (one front, one rear). If the rear differential is a "posi-trac" or "limited-slip", then both axles should lock and drive the vehicle (hence, three-wheel drive), but this style differential is not as common as it once was.

The gears in the axels are open type - meaning they drive the wheel with the least amount of traction, most often right rear and left front wheels. Some of the rear axels were fitted with a limited slip type that would drive both wheels.

the noise is coming from the clutch plates in the differential, i am assuming that it is posi-trac. and not a limited slip. you can get rid of this noise by draining fluid and replacing with proper differential fluid as recommended by manufacturer (go to gmc dealer parts dept.) also ask for posi-trac additive, use two bottles, the noise will not go away instantly, you will need to drive it for at least 500 mile before you notice change,

000 DODGE TRUCKS DURANGO 5.9L 8-cyl Engine Code [Z]
Limited Slip Differential, Rear 8.25-9.25 W/ TT......GL-5* All TEMPS......75W-140
Standard Differential, Rear 8.25-9.25 W/ TT......GL-5 All TEMPS......75W-140
Limited Slip Differential, Rear 8.25-9.25 W/O TT......GL-5* All TEMPS......75W-90
Standard Differential, Rear 8.25-9.25 W/O TT......GL-5 All TEMPS......75W-90
Note:Trak-Lok axles require Mopar limited slip additive limited slip additive 04318060 or equivalent
Differential, With 7.25 RingGear Rear..........1.4 liters Fill no higher then 3/4 inch below plug hole.
Differential, With 8.25 RingGear Rear..........2.1 liters Fill no higher then 1/4 inch below plug hole.
Differential, With 9.25 RingGear Rear..........2.3 liters Fill no higher then 5/8 inch below plug hole.
Thank you for using fixya and good luck

Sounds like you have a limited slip or " Posi-Traction" rear differential, if this is the case than go to the GM dealer and ask them for a bottle of friction modifier oil for limited slip differential. This stuff is pure whale oil that helps to lubricate the clutches in the differential. After adding the lube find your self a big empty parking lot or other paved surface and drive the vehicle forwards then backwards in a slow figure 8 patern, turn as tight as you can each way, this will force the clutches to work and help limber them up. The differential might make some crunching sounds, but the noise should quit as the lube gets in and does its job.

No. Power will transfer to the wheel with the least amount of traction unless the differential is a limited slip diff. You likely have limited slip (Positraction) in the rear diff so both wheels will spin. The front axle doesn't have posi so only one wheel will spin. (3 wheels spinning)

It is possible, you just have to know what gear ratio you have in your Sierra. I had issues with my son's rear differential and did the Salvage Yard and picked one up for $250.00 with less then 45,000 miles. Remember new cars end up at Salvage Yards also.

Here are the Pro code for the rear ends to your Sierra and you can match one up at a Salvage Yard.
GQ1 -- AXLE REAR, STD RATIO
GT4 -- AXLE REAR, 3.73 RATIO
GT5 -- AXLE REAR, 4.10 RATIO
GU4 -- AXLE REAR, 3.08 RATIO
GU5 -- AXLE REAR, 3.23 RATIO
GU6 -- AXLE REAR, 3.42 RATIO
G80 -- AXLE REAR, LIMITED SLIP (POSI TRACTION)

HC4 -- AXLE REAR, 4.56 RATIO

Open Your glove box and look inside it. Should be a list of codes on the bottom.
Example: GU6 G80 According to that, you'll have a 3.42 posi

Good luck and keep me posted and call around Salvage Yards, there prices will differ from one to the next salvage yard and don't ask them for a posi rear end. The cost will you more, just search all the SUV's and look at the pro codes in the glove box. Hunt, most awd system SUV will have the G80 rear end.

Good luck and keep me posted.

Your explanation is stating two different rear end styles. Limited slip and posi-traction. But either way if you have a wheel that won't engage when one slips with limited slip or one that doesnt turn with posi then you either have a broken axle or an internal differential issue which can be confirmed by pulling the rear cover off the diff.