My Kumho SAT's did the same thing, and I can tell Charley that it had nothing to do with tire pressure in my case. I bought them in Autumn, and they were great in their first winter. The following winters were much more disappointing and utilized the same pressure as the first. Many years of my own experience playing with tires in WI winters vehemently disagrees with Charley's conclusion that pressure reduction is beneficial in winter, but it's not hard to do your own experimentation to see for yourself if it helps or not. It doesn't take long before that new, supple rubber hardens due to UV exposure and repeated heat/cool cycles--it happens within a single year--and I have no doubt that was a major factor in my case. Tread wear was also likely a factor in my case as I put 12-15k miles on per year--that's a fifth to a quarter of the tread gone in the first year.
I've gone back to using a winter tire set in winter. Other than storage, there's really no solid reason for anyone not to. In the long run, it's not any more expensive to you since driving on one set means preserving the other, so all your tires last longer time-wise and last just as long as they should mileage-wise. I swap sets during an oil change when I'd already be doing a tire rotation, so it's not even any extra work for me. I do not use studded tires for two reasons: they're illegal in WI; studless tire technology is to the point where many studless winter tires are consistently outperforming studded tires in most conditions even including raw ice. Studs are becoming more and more of an exception than a rule in terms of winter traction. People don't experiment and test winter tires as much as other tires though, so word of which are the great ones and why doesn't really get around as much.
Build Thread -- http://www.jeepforum.com/forum/f177/whats-chrokeese-build-thread-2525690/