DRIVING DOWN THE ROAD MAKING A EASY TURN TO THE RIGHT, TRUCK DARTS TO THE RIGHT ALMOST TAKES ME TO THE DITCH. IF I HADN'T BEEN ON MY TOES I WOULD HAVE CRASHED BAD. CALLED MY DEALER WHERE I PURCHASED THE TRUCK, BOB PULTE CHEVROLET, I WAS TOLD TRUCK WAS NOT COVERED FOR A REPAIR. I WENT TO A LOCAL MECHANIC, WAS TOLD TO PULL THE POWER WIRE OFF THE BACK OF TE POWER STEERING PUMP. I DID THAT AND PROBLEM WENT AWAY. I HAD SEVERAL CLOSE CALLS BEFORE FINDING OUT HOW TO FIX THE PROBLEM. I FEEL GM SHOULD HAVE RECALLED THESE 1998 TRUCKS AND REPAIRED THE STEERING PROBLEMS. SEEMS TO ME THAT GM JUST SOLD THOUSANDS OF PEOPLE THESE TRUCKS KNOWING THIS PROBLEM EXISTED.

I had this happen to me this summer while towing my fifth wheel camper. Didn't at all like what happened, as it was way too easy to over steer the truck. I did some homework online and talked to a few auto parts stores around town. They said a common failure is the "steering wheel speed sensor" which is located at the base of the steering column. It's a small, grey plastic round shaped thing with a 3-wire harness coming out. This little guy activates the speed compensated power steering. When it's worn, it thinks it should have more power steering, even while traveling at highway speeds. This is what gives you the lurch, or the over steer. I replaced this, and voila! It worked. I did all the same as you did; had the suspension looked over, but never replaced any parts. My truck has all original shocks, ball joints, tie rods, etc...It's never been off the highway. Take note that this part is usually only available at the GM dealer, and cost me roughly $140. Hope this helps!