My stockers wore out in 16k, due to over-inflation. The centers wore out. My findings have been that the Goodyear Wrangler SR-A's need to be inflated to about 28psi, which will set off the low-tire warning lights. I have about 6k on a set of replacement SR-A's that I run in the winter, with no signs of wear.
It sounds to me that your problem is UNDER-inflation though. How much air do you have in them? If you rarely haul anything, I suggest running about 4# more in the fronts because that is where the majority of the weight is.