Hello everyone, this is my first post, so be easy on the rookie!  I recently returned my 04 Silverado when the lease was up, and bought a truck I have always wanted.  My new ride is a 99 2500 Chevy(the old, old body style), 350, NV4500, 10.5" rear end with the G80-blech
My 04 was a two wheel drive 1500, extended cab, short bed with the 5.3, that truck ran like a raped ape.  I am disappointed with the power of my 350, granted the 2500 is probably heavier, and has 40 less horsepower, but I feel like I need to do some engine work to get the power up a little.
I plan on keeping the CPI, and emmision legal.  What's the deal with no aftermarket intake manifolds?  Is this the first and last small block with no a/m intakes?  Would a higher ratio rocker w/roller tips have a noticeable difference in power and keep it legal? Shorty headers and a cat back are already on order, btw.  I am on a relatively limited budget, so bang for the buck is what I'm looking for.  
Any other suggestions that you guys have had personal experience with would be appreciated. My apologies if this a topic that's been beaten to death. I checked a couple of pages and didn't see what I was looking for.
Thanks everyone  

First of all if you are looking for power, shorty headers is the wrong move! If you really feel you need a header, you want a long tube header (1 5/8 dia x 34 long) or a Thorley Tri Y as these can boost midrange power. Shorties will take away from it and reduce response in town and MPG. Personally I would not waste the money on any one them if budget is limited. Before you start bolting things on truck you need to figure out where you are going with it. Axle ratio vs tires size play a big role in over all performance and even more so with a stick (the 5.3 had a deep first gear in the 4L60 together with a some what "loose" torque converter (higher stall and torque multiplication) that helped it get going. (the 5.3 was never offer with a stick and one reason is that it lacks lower RPM torque the tranny and converter makes up for) You do not have that tranny boost so to speak. I own a Vortec 350 in a 2000 K3500 I bought new (they were still old body style for 1 ton models) and I know the engine well. It does its best work above 2500 RPM and runs very strong up to about 5000 RPM. I do run at least 89 octane in mine all the time and I can tell a difference as 350's are prone to knock but you do not know this because the knock control retards spark before you hear it but it does effect overall power and response. You might consider a after market tune as it responds to that but I cannot stress enough that if you want good results here, you must use at least 89 octane. You will feel more bang for buck with a tune and 89 than headers. (BTW, shorties if they offer any gain at all it is above 5000 RPM and are purely cosmetic) If you want most bang for your buck focus on a after market tune and axle gears and you will not be disapointed. The minimum axle ratio you want with a stick and stock tires is a 4.10 (a GT5) but a 4.56 would be better. If you are running bigger tires a 4.10 is going to hurt you and depending on tire size you want at least a 4.56 or 4.88. The Vortec 350 is not a weal motor but coming from a automatic to a stick is a big difference because you lost torque converter boost and stall. Deeper gears will help a lot with this. Headers and a different air filter will not. BTW, I have a automatic and stock sized tires on my K3500 and it currently has 4.10's in it but I have a new set of 4.56 gears sitting on the shelve for it too. (not for bigger tires but for even more power because I drive and use a P/U as a truck not a ride)  

Thanks for the advice SnoMan.  I am looking for low to midrange torque.  I have heard the LT4 cam is a good computer friendly cam as well-have you heard the same?  

There is more to be gained here with a better tune and higher octane fuel. The cam you suggest has more top end power but at the expense of low end power which you really need with a stick. With that cam you will have less below 3000 RPM. Better fuel would allow for a better spark advance curve and more response and power and better overall MPG. I have a simple Hypertech 3 tune on mine and use 89 as lowest grade and sometimes 93 when it is really hot out. I can tell a difference in response with the tune and it improve my in town average about 1 MPG as far as I could tell. I have not had it on many trips but it does do about 17 or so on road and has good power if you step into it to pass.  I got my tuner off Ebay cheap a few years ago and that tuner lets you teak speedo to dead on too. One word of caution with any "tune" do remove it from truck if it ever goes to dealer because dealer scans or flashes ECM (which they usually do because they are "looking" for things wrong for revenue and never tell you they scanned it unless they find something because they are supposed to charge for a scan so they do not want you to know you got a freebie) This can kill tune and render tuner unusable as they usually marry to a VIN number and divorce from it when you remove tune with tuner and if dealer over flashes it the tuner thinks it is still married to VIN and faults when tune is not found plus it will not reinstall even in another vehicle because it has not been "divorced". The VorTec 350 is a good motor and with good gas, tune and gears it will not disappoint you. I know the urge is to use cheapest possible gas you can find but that engine runs better with 89 or more and the knock control is so good that it detects it before you hear it so you do not realize what you are loosing sometimes when timing is retarded to control it.  

Ok, I know one of the reasons it feels so sluggish, after driving it now for two weeks, right at about 1800rpms the engine just feels undertimed, like there is not enough advance-real flat.  
So I took your advise SnoMan and ran the 87 octane out almost bone dry, and just filled up with 93.  I was skeptical that a higher octane would make much difference in an engine like this. But I am telling you what, there is a huge difference in power and acceleration.  That flat spot is all but gone.  I still think this weekend I am going to stick a timing light on it and see exactly where I am at.  Do these vortecs have a mechanical advance?  Sorry to ask a stupid question, this is the first Vortec I have had.
I did find headers finally that would fit-Thorley Tri Y's.  Getting ready to make that purchase...  

No such thing as a stupid question in my book. The stupid part is not asking if you do not know. Timing on vortec is electronic and tuners tweak it some. Problem is the knock sensor is so good at hiding knock that it steal your power on 87 octane which out you knowing it because it is not knocking but only running sluggish. 350's are prone to knock on low octane fuel because on large bore to stroke ratio, CR and combustion chamber design and respond well to better gas. The 4.8 and 5.3 have a longer stroke and smaller bore and this makes them a bit more tolerant of lower octane fuel but it still helps them too. You might play around with 89 or 90 octane to see what you need (where performance suffers) but I generally use 93 in hot weather and 89 in cooler weather and never use 87 regardless of cost. BTW, the Tri Y's are the best street header you can run in my book.