My A/C my tension pulley continued to vibrate at low speeds until it finally broke. I replaced it to only have it happen again. The root of the problem was the A/C compressor had sludge in it which caused it to put harmful strain on the tension pulley. I replaced the compressor, drier and orifice for under $350 (DYI. You can purchase a new kit online for about $225 (all items included. Be sure to replace the orifice and clean out the lines, so that no debris finds its way back to you new compressor. YouTube has a great series of videos on how to change your A/C compressor, drier and orifice. you can save yourself at least $700 by doing it yourself.
Also, have a shop evacuate your system of any coolant. I had my system evacuated and refilled for under $100 at a Valvoline Oil change facility (included in the $350). This is a common problem with this vehicle, although I can't complain, 195K is a lot of miles. I bought my Yukon new and have enjoyed every mile and wouldn't hesitate purchasing another one.