The stretch fit belt for the A/C is cake. Just don't do what I did and waste money on the Gates install tool because I couldn't make it fit my crank pulley. A couple zip ties got the job done instead. I converted both our SS's years ago, no issues, and we run the A/C all the time being SE Texas ya know.
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Looked up the belt number using a GMT900 6.0, I wanna say 2009 or 2010 3500. This # fit our 2006 6.0 (LQ9) engines, not sure how universal that will be across the board though. One less tensioner and pulley to go bad = win
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Richard