Mom's ride

I recently purchased a used 2007 GX 470. It has a lot of steering vibration in the "Comfort" setting. It improves when I put it into the "Sport" setting to the far right on the dial. There is not a Lexus dealership in my area, so I have it right now with a Toyota Dealership. The Tech working on my truck says he has driven a GX 470 with the TSB-DL 001-08 problem. He says he is positive this is not the same problem. It sure sounds like the same problem. When I first drove it, I thought replacing the tires would take care of it. I purchased my standard 4wd vehicle tires for it. The shaking immediately improved, but not completely. We own about 7 4WD trucks, none of them shake like this Lexus--the Luxury Truck. Does anyone have any other remedies?