One problem related to differential unit has been reported for the 1999 GMC Yukon. The most recently reported issues are listed below.
Had taken vehicle to dealer for brake service on front disc brakes due to wear on disc. Work after 15000 miles had to be performed again due to disk wearing out. Consumer believed that brakes were not heavy enough for vehicle. Disc warped causing vibrations and brake failure. The disc was turned a t 15k miles and was replaced at 28k. Transmission does not hold on hills. Front end was leaking due to front pinion seal failure . .