Sylvania has HID replacement headlamps for Chevy and other trucks, but not GMC.
www.sylvania.com/xenarc
The Sylvania kit will not fit for the Yukon, as the Chevy headlights are not as tall as the Yukon ones. (sigh...).
They do have a rectangular fog light / auxiliary low beam light kit.
That fits the Yukon, but not the Denali, which has round fog lights.
http://www.sylvania.com/xenarc/x1010.htm
So, I will take tonytone's advice and get the Denali (projector) lamps and then add an HID bulb kit.
Who has quality Philips or Osram HID kits?
Thanks again, Eggert.