Personally, I would go to ECS. They tuned my car when I had it and I was incredibly happy. Do you know if the car had ever been tuned? Frankly I'd sell the diablosport because I have never seen them to be very useful at all. The lid will be good enough for now, but I would look strongly into an LS6 intake, they can be had for ~350 shipped at most on the forums. I wouldn't tune before getting all the parts on that you want. Just my opinion...
-J
EDIT: oh and congrats on the car