Ok, I will start it off now that I have all my information.
40k miles on the 2008 Canyon 3.7L (bought it new, traded in the 04 Canyon) My truck was built 6/2007 (stamp on the frame)
Symptoms were: Rough idle and Check engine light (PO300 & 303) at idle
Just got my truck back from GMC, they reported the intake valves on #3 were not seating properly. There is a bulletin internal to GM about specific VIN #s affected to the 3.7L (cylinder head problems). My truck fell in that VIN break, along with all the troubleshooting information that lead them to replace the entire head under warranty.
I am sure that I am not the only one out there.. Hope this helps out anyone! I hope this does not spur on "panic attack" but educates any 3.7 owners to bring the truck in if your idle gets rough + CEL comes on. The head issue does apply to certain 3.7s, GM has a redesigned head to address the problem.
Funniest part is that I went through a defective cylinder head on my 2004 Canyon 3.5L... Not fun enough doing this just once! Although, GM has enough information and specialty tools that you will not be out the truck more than a day or two (much improved since the 04 went in)...
Any other 355Nation 3.7L owners?