That’s actually a fairly common swap on other performance oriented forums and it’s supposed to be worth an extra 20-30+ HP on the 6.0 engines depending on who’s dyno sheet you’re looking at. They flow as well or better than the LS6 intakes that everyone goes nuts for but they’re a lot cheaper and have longer intake runners to maximize low end torque. FYI though the TBSS and other Gen IV truck TB's are 87mm, only the cars got a full 90mm but the couple of times I saw someone try to swap to a 90mm TB there was virtually no gain...
As far as whether or not it's worth it, that's up to you to decide. I was able to find one complete with injectors, rails, TB, etc for only $140 and since I was already doing a new cam and swapping on some 243's I figured why not? Here are a couple of things to look out for if you’re thinking about doing it:
-If your truck is set up for a cable TB you’ll either need to buy a new 90mm 4 bolt cable operated TB or a 3 bolt to 4 bolt TB adapter plate to re-use your existing 78mm TB. Most people aren’t a big fan of the adapter plate option because you wind up limiting the flow of the new intake with the smaller TB.
-If you’re running a DBW TB you’ll need some sort of the harness adapter since the newer TB has different electronics. For your 03 engine you’ll most likely need an X-Link harness adapter from Torquerush that runs $235 but is basically plug and play. There’s a cheaper $50 harness from Caspers (and a few others) that will let you use the 90mm LS2 throttle body but you also need a 99-02 TAC module and both of those can be pricey. Some of the aftermarket harness makers might also be able to build that in to your custom harness if you ask for it. I talked to BP Automotive and they said they could make me a harness that would work with the 87mm TB that came with my intake but I would need the 99-02 TAC module as well which wasn’t a problem because I already had both style TAC modules laying around my garage…
-Fuel injector plugs are also different. You can pick up some plug/harness adapters or new plugs with pigtails to splice in to your existing harness pretty cheap. Or if you're going with an aftermarket harness just request the newer style plug when ordering it.
-The newer intake also has a return-less style fuel rail so if your truck isn’t set up that way you’ll have to figure out something there but there's a ton of different ways to do that and none are all that complicated. Plus if you’re swapping the engine in to an older truck you basically have a blank slate and can do whatever works best/is easiest for your situation.
Lots of information on this can be found online by searching for “TBSS intake swap” but here are a couple of threads I bookmarked back when I was reading up on it:
http://www.gmfullsize.com/threads/ho...e-swap.264691/
http://www.performancetrucks.net/for...ll-nbs-493269/