For a $3,700 dollar amount for this 2003, consider the money saved on a very new version, you could invest into transmission / engine issues and still save money? I am glad I got a 4 WD instead of AWD ( from what I read about AWD)..... My 6 month old 140,000 mile, 2005 Yukon XL SLT 4WD was well serviced & well taken care of.
Before buying it I checked the service record through the GMC dealer and all scheduled work & early warranty stuff was done. There was no "evidence" of UN-documented work underneath it. ( There was no rust either)
So, have it checked well, by your trusted mechanic... It could be a good deal!!!
( Up-date)..... I read your latest post..... I did notice the rust in some of the photos...
If that was the case, as you said..... run away!!