I just returned from a large construction trade show out west. An LBZ display model was there as well as a couple GM engineers. I was refered to the "expert". He has asked me not to use his name and was supposed to have been involve with the development of the medium duty truck as well as the Duramax down to every nut and bolt. When I questioned him about the over heating problems with the LLY he didn't seem suprised at all. He told me that the impeller on the LLY was a redesign and moved more water at a faster rate through the block and was not allowing the coolant properly cool the block and that it was wreaking havock with the thermostats making them constantly cycle. It seems to make sense. He then said if I had been to the dealer with over heating issues to have an LB7 water pump installed. I remember reading at one time that the part # was the same for the LLY and LB7 water pump. Has anyone verified this or is this guy blowing smoke up my a** to get rid of me? Has anyone tried this?