the 5.3 doesn't really have enough airflow to warrant even the ls6 intake, honestly. Unless you have a really raunchy cam in it or something. The camaro/corvette ls1 intake flows plenty of air for a stock(ish) 5.3. Now if you are considering doing anything bigger in the future (347/383 out of that block, or a stockish 6.0 or 408), you'd be better off going big now so you don't waste time and money.
I got my ls1 intake from a guy that upgraded to a BBK with his 383 LS1 for $20 with his stock fuel rails, and his 383 picked up 18 peak wheel horsepower from the stocker. The 5.3 might pick up 1/2 of that, but I'd prefer spending the extra $280-480 (depending on where you get an intake) on stuff that would net me more than 9 ponies.
Something to consider is that you'll need to run the longer ls1 type injectors in any intake/fuel rail upgrade (I think the exception is the ls2 intake, but don't quote me on that), the coolant crossover will need to be changed (may as well do the ls6 type now, it's cheap) and you'll need to get injector adapters to adapt the delphi plug to the EV1 plug. I also changed the accessories to the f-body stuff so they would work with the car intake perfectly. I think you can run the truck stuff if you get inquisitive, but I didn't feel like messing with it.