One problem related to differential unit has been reported for the 2003 GMC Yukon. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2003 GMC Yukon based on all problems reported for the 2003 Yukon.
Front differential fails on awd versions of Yukon/denali models. Unusual front driveline noise is experienced especially during light acceleration or load. Noise is a whine type of load. This one failed @ 54,000 causing dealer to rebuild front differential with new bearings and seals. Old bearings were badly scored and one of them broken to many pieces. I asked for parts and was given what could be pulled out. Internet search indicates many owners with awd systems which were also available on Yukon as well as denali models have had similar failures. Cost to repair as warranty expired at 40,000 miles was approx. $1000.