When do you think that there will be intake/exhaust/PCM mods for the V8? I've been searching without any luck. How long was it until the I5's had mods?

 

The 5.3 is a LS4 so you could check into Diablo Sport programmer/Tuner, Larger Throttle Body, Heads, Supercharger:
Lingenfelter GM SUV Supercharged Engine Package 475 HP 2001-2006
Lingenfelter GM SUV Supercharged Engine Package 500 HP 2001-2006
Lingenfelter GM SUV Supercharged Engine Package 2007 coming soon
Lingenfelter 427 CID Twin Turbo Engine Package 700 HP 2001-2007

Remember COMMONALITY, the 5.3 LS4 is in the GTO too.