12.5 is really wide, I know I could not run those on my 05 Yukon, I'm running 285/65/18 and that is as wide as I can go without rubbing with a stock suspension, 285 is just a touch over 11 inches wide. But as your staying with the stock rim diameter it is possible that you might get away with it. A tire dealer can tell you more about clearances on your rig, this is just my experiences with my rig. HTH
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