um........they do make longtubes for the new trucks guys.
http://www.americanracingheaders.com/
american racing headers makes them (and for teh initial poster, they're in amityville, ny) Having owned 3 heavily modified vettes (550-800 rwhp) in teh past 6 years, I've tried most of the options for vettes and these are without question the best. I've seen the headers installed on an 07 denali locally, and as to be expected they're top notch stuff.
talk to nick but with a 5.3 and no boost I'd stick with 1 3/4 personally, more cubes and boost I'd go bigger. Probably also going to want a catted system, no cats gets a little old and winds up a little loud as well.
Don't even waste your money on shorty headers from JBA or Edelbrock, I've had to rip those off of trucks already for cracks and rusting out over time.
If you wind up picking up a set and need them installed let me know I'm in queens and can probably get them on for you.
as for a supercharger, my truck was a R&D pig for a supercharger company in jersey (and was going to american racing to get used for mockups until one of the owners bought an 07 tahoe) its on a buddys avalanche with a 408 right now but if you're local you might want to check it out.
