Congrats on your new GXP man.
4% in 10 days isn't bad. thats a 25th of your oil life...so 25x 10 days =250 days. And it'* set high by GM. Should still change every 3 months.
I was worried about stagnant oil also and put 500 "breakin miles" and took to dealer and swapped out for synthetic. The N* is an extremely tight engine and you might notice a little smoke when ya start up. Mine really opened up at about 700-800 miles.
Also the N* losses between 1/2 to full quart between changes so keep it monitered.
The N* PCM is Locked and unflashable.
Like corvette crazy mentioned, most HUD'* I've seen can be off a mile or two. quite a few GXP'* it seems have a vibration problem. Fixing it is a dealer item and covered by your warranty. And I think your aware that if you pull the dash apart to get at it, you'll likely void that warranty.
Will gets around to everything. He'* a very easy going acessable person, and doesnt mind you PM'ing him. And if ya get to be a pain 'he'll tell ya
all cars have design flaws , and ours is certainly no execption but most of us love them anyways