Electric Power Assist Steering System problems of the 1998 Chevrolet Suburban

1) near crashes have been caused by an erratic condition in the steering. Called gm national customer service number and gave all information and was promised someone would contact me. (never happened) 2 other families here in rochester have the same vehicle and the same problem. 2) upon turning the steering wheel, the wheel itself suddenly free-wheels several inches. This rapidly accelerates the degree of turn and makes the driver feel as if they have lost control and the entire vehicle often swerves out of control. 3) I brought it to 2 dealers here in rochester and neither was able to detect the problem on a test drive. The problem comes and goes. When it happens, it will scare the living out of you, and the driver on the other side of the road. We have all but lost control on more than one occasion. A friend of mine who also has a Suburban said he had the same problem and finally someone suggested replacing something called the power steering assist? we have a 98' Suburban and have had it since it was 7,000 miles old. It has a 350 and is an lt and has 3rd seat and four wheel drive. I think this problem affects most if not all Suburban's in our year class. Chevy is not responding to my questions. Please help.

Steering sensor failed, causing steering wheel to skip when turning and feels like control of steering is lost momentarily. Sensor was replaced once and problem was cured for a time, but it is now recurring.