in my experience with this one.......the tailpipe has been extremely sooty black since I bought the truck and installed the Van Aaken chip. Have never had to add oil between changes (changing oil at approx 22000 to 25000k). Since we hardly ever use more rpm than needed to get down the hwy..didn't notice any loss of boost or power otherwise.
on a side note: the 06 with the SCT is still harder on fuel but the tailpipe is clean...go figure. Having said that, we are noticing a improvement with the SCT but haven't logged enough miles to give a report with any accuracy.