[Big Tex]

I would check your rear u-joints first. I had a 6" lift with blocks on a k5, and had the same issue. It turned out to be a bad u-joint. Has the truck recently been lifted? If so, an alignment shop can fix the steering with an alignment. If the truck has been lifted for a while, then it's something else like mentioned above. I ask because when I installed my lift, the steering wheel was way off, and would only turn about half way one direction. And, the probably already worn u-joint, popped it's head up shortly after. The new angle on the driveshaft probably magnified it. Hope it helps.....