Build date on GMC Yukon XL was week of September 11th and traveled by rail to Virginia. I received it week of October 13th. No issue with car. I'd certainly notice it.
Just figured I'd chime in - ordered my Yukon XL in late August from the factory. It went into production mid September and arrived a week or so ago. I have not experienced any of the issues mentioned in the thread. I'm impressed with build quality, as a previous owner of a Mercedes GL 450. It's among the nicest cars we've owned as a family.