Actually guys... I'm with you on how you feel, BUT DON'T YOU KNOW WHY THE TIRE STORES ARE SAYING THAT??
They really are just trying to protect themselves of any possible liability! Have NONE of these retail stores given straightforward reason to you?? The Costco up here in Canada will sell me "oversized" BFGs but WILL NOT mount and balance the tires for me.
They say they have to follow the manufacturer's specifications. I guess that follows with the same reason with the possiblity of voiding a part or all of the manufacturer's when you lift your truck. yes, it sucks...