Hi, my research indicates you can install a single din aftermarket head unit in the 2001 Yukon.
A couple of good websites to use are crutchfield and modifiedlife.
Crutchfields will identify exactly what adapters are needed, and modified life has the factory wire colors.
You will need an adapter to fill the space between the aftermarket stereo and the hole left by removing the factory head unit.
You will also need an antenna plug adapter.
I recommend you buy the wire harness pigtail to simplify the installation--this may or may not include the antenna plug adapter.
If you have onstar, you will need an additional adapter.
If you have steering wheel controls, you will need another adapter to keep those.
Keep the above things in mind when selecting a new aftermarket stereo, as you will need one that is compatible with steering wheel controls and onstar, if you have either of those and want them to continue to work with the new stereo.
Crutchfield has an link called "outfit my car" that takes you through a "Turbo tax" style questionaire and tells you what will work and what you will need. here is the link: http://www.crutchfield.com/App/Car/outfitmycar/MyCar.aspx
Assuming you have a base Yukon, here are your factory wire colors from modifiedlife.com:
2001 GMC Yukon Car Radio Wiring Schematic
Car Radio Battery Constant 12v+ Wire: Orange
Car Radio Accessory Switched 12v+ Wire: Yellow
Car Radio Ground Wire: Black
Car Radio Illumination Wire: Brown
Car Stereo Dimmer Wire: Gray
Car Stereo Antenna Trigger Wire: N/A
Car Stereo Amp Trigger Wire: N/A
Car Stereo Amplifier Location: N/A
Car Audio Front Speakers Size: N/A
Car Audio Front Speakers Location: N/A
Left Front Speaker Positive Wire (+): Tan
Left Front Speaker Negative Wire (-): Gray
Right Front Speaker Positive Wire (+): Light Green
Right Front Speaker Negative Wire (-): Dark Green
Car Audio Rear Speakers Size: N/A
Car Audio Rear Speakers Location: N/A
Left Rear Speaker Positive Wire (+): Brown
Left Rear Speaker Negative Wire (-): Yellow
Right Rear Speaker Positive Wire (+): Dark Blue
Right Rear Speaker Negative Wire (-): Light Blue
Please let me know if you have questions, and thanks for using FixYa.