Another change for the GMC Yukon and Yukon XL is the 'GMC' badge on the rear hatch has a thicker chrome trim around the red 'GMC' letters.

2000-2003:
http://gtcarlot.com/colors/car/46318078-4.html

2004-2006:
http://gtcarlot.com/colors/car/37777420-4.html

This also applies to 2004 Sierra pickup trucks, while Envoy and Envoy XLs appear to have received the newer badge for the 2003 model year.