Carrier/rack problems of the 2009 GMC Acadia

The vehicle has been looked over by many mechanical professionals. At slow rates of speed, intermittently the steering will stiffen and lock up making it very scary when driving. We have been told over and over that rack n pinion and pump are fine. After researching, this looks like a typical issue. Is there anything that gm can do for this?.

Vehicle had a slight misfiring when climbing incline. We replaced two spark plugs. Misfiring calmed down. A couple days later misfiring resumed. Husband was driving daughter to daycare when car had multiple dts codes appeared (stability track, check engine, reduced power) with car suddenly stalling while on a highway leaving barely enough time to coast off the road and out of the way of traffic traveling 60mph. GMC refused to assist us on this issue until we found online a TSB about the timing chain which had broken. Due to the constant misfiring (direct result of the timing chain) two of my catalytic converter became clogged. Those have now been replaced out of my pocket however when driving vehicle home while it does run smoother it now misfires all the time even when not going up hills and idling very low and misfiring while idling. I am scared that while driving my vehicle this may happen again because the issue has become worse.