Regardless of what the manual says, I really recommend changing differential fluid every 24 months or 30,000 miles. If the vehicle is used to tow/haul quite often, this can increase internal wear on the differential. Remember, the Yukon is only a half ton truck.
The most common cause of differential failure are stress and heat. If you do a lot of hard driving like towing, 4wheeling, or burnouts then a differential can fail.
Shock load is most typical failure. This is caused by spinning the tires in mud or snow, the tires then suddenly get traction, this causes such a shock, parts snap.
Either water seeping into the differential. If it has been used to launch a boat semerging it can cause this. Or it may not have enough fluid. Causing excessive wear.
given below following steps causes a yukon rear differential to go bad if we drive the vechiles always in the hills & bad condition road make differential to go bad