What has to be modified to install a NNBS/TBSS intake on an NBS truck, and what does it gain?

What it gains: on a cammed 6.0 LQ4, Richard Holdener's test showed about 12–13 hp over the Gen III truck intake, with two different cams:

6.0 LQ4 test (Holdener)	Truck intake	TBSS intake + 90mm TB	Gain
Low Buck Truck cam	439 hp / 453 lb-ft	452 hp / 457 lb-ft	+13 hp / +4 lb-ft
Truck Plus cam	453 hp / 448 lb-ft	465 hp / 457 lb-ft	+12 hp / +9 lb-ft

Among factory cathedral-port intakes, back-to-back testing puts the TBSS (TrailBlazer SS) intake on top, but it's tall and often won't fit low-hood cars — which is where the LS6 intake comes in. The truck, LS2, LS6 and TBSS intakes all work well; the original LS1 intake is the weak one. An LS3 (rectangle-port) intake on cathedral heads with adapters is a poor choice.

What changes: the TBSS intake takes a larger throttle body (a 90mm unit in the test; a 3-to-4-bolt reducer adapts a factory truck throttle body) and it's tall. We don't have a source listing the full modification list for a specific NBS truck, so confirm sensor, fuel rail and throttle details for your year.