Another issue people encounter with the GXP is higher usage of oil. It deals with Displacement on Demand crap. A simple tune to remove the DoD, and no more issues. Not like it uses a crap ton of oil, but a littlmore than normal. Plus removing it you may lose 2-3 mpg at most.
Either it uses quite a bit or whoever did my oil change before I got the car didn't put all the oil back in. One way or the other my GXP was almost 3QTs low on oil.