I know this is old. Please enlighten me on this process. Is there a thread I am not finding?

 

The issue people don't understand is a larger intake manifold won't add power, it can only free up power. It is the same concept as larger free flowing exhaust. Sure a dual 4" straight pipe with long tubes with 2" primaries sounds great in theory, but it will lose power torque if the engine can't take advantage of the new found flow. I think the power needed to see a gain from a TBSS manifold is around 350rwhp. So if someone were to make 300rwhp in a mild cam 5.3 then no they won't see gains just like a stock 4.8 won't see much gains from long tubes and a 3" straight pipe exhaust. Now take the same 5.3 add an aggressive size cam, good heads, and a 150shot of spray. I bet that build picks up 3 tenths with a TBSS intake vs truck intake. In the case of the OP I think the build simply needs to be dialed in and will see improvement with this intake. I would investigate throttle body position on wot runs as the 87mm tbs have been known to be finicky.