LT1/LT4 manifold ???
You can convert the LT1 intake to be used on any SBC. The bolt holes have to be redrilled and a hole for the distributor has to be made. But it will work fine. And once you do so, you can upgrade the injectors no problem, assuming you use the LT1 rails.
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From: Decatur, TN (N-W of Athens)
Assuming the 99 doesn't use the GEN III block, but I'm thinking it's still that CSPI (updated CPI, S = Sequential). If that's the case, it should work yea. If you're good at wiring, you might even be able to hook up the CSPI harness and create an adapter harness of sorts to plug into each of the 8 injectors so you don't have to run an aftermarket computer. I'd recommend finding the 92-93 LT1 intake though, just because it's prettier 
And doesn't have a silly hump in the middle for the dumb fuel rail. Yet the 94-97 MIGHT work better with a distributor due to the fuel rail change. Dunno :\
And doesn't have a silly hump in the middle for the dumb fuel rail. Yet the 94-97 MIGHT work better with a distributor due to the fuel rail change. Dunno :\ TECH Senior Member
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Joined: Oct 2006
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From: Decatur, TN (N-W of Athens)
again dude if you read this 
Anyways, if the LT1 cam doesn't help, or the computer can't compensate w/o a tune (some cams don't need one and the comp can do quite well still) then you'd either just take it out or get the thing tuned
Is it the CPI motor thats in your truck? It's a good chance, but 99 I believe was the last year of CSPI, so you could have a newer block. Easiest way to tell would be the exhaust manifolds. If you don't know the diff, old school is O-OO-O ports, and GEN III/IV blocks are O-O-O-O layout. If it's the latter, you have the better engine and your options are opened WIDE for performance
1999 tahoe would be the 5.7. GM didnt use the ls based design on tahoes until 2000. <--- but i believe you could buy a tahoe limited in 2000 that was the retro design... someone correct me if i am wrong. And formula, not a prob man. anything to help a fellow ls1tech member. 
