I started getting clunking noises hitting bumps etc and we found the pivot pin assembly had vertical movement about 1/2" so we replaced that. Then multiple clunks (different than before) started. Two or three on start up and stopping. Took it to front end place yesterday and they said steering box was shot and that they are notorious for going out and the bad part is they are under constant pressure lubrication so the failure is directly not attributable to poor lube maintenance. This is a 979.00 repair and apparently the failure rate is so high that all the parts places offer rebuilt steering boxes about $250.00 cheaper than the dealership. It would appear either the design is bad, the power steering lube folks make poor lube or the materials the box uses internally is designed for a early falure. the entire rest of the front end is fine. This is very disturbing in that the rig only has 117K on it and I don't understand why GM engineering has not addressed the problem. I am also told there is so many metal particles generated into the lube and circulated through the system that the lifetime warranty suppliers require a new power steering pump be installed with new steering pump and the rest of the system flushed well. This is very disconcerting as I love my 2007 2500HD and until I know the problem has been cured I won't even consider a new one. Does anyone have any information on the failures, a fix or a better power steering lube? This seems like it would be a simple problem to fix if anyone was interested in a long system life. After all so far as I know the engines are good, trannies are good and rear ends or good but this has got me stumped.