What is the stock hp of your 5.3L 1999 Chevy Silverado and what are some ways you would recommend to increase horsepower?
270 H.P. & 215 Lb/Ft of torque. There is no easy way to increase power. Dual exhaust system will help somewhat. Free flow air filter will help at high rpms, but not much. You are pretty much stuck with the stock power without making internal engine modifications. Of course you could install Nitros if you want instant power but at a cost in reliability and possible engine damage. Get a programmer. They can be kind of expensive but its easy and you can tune the computer to how you want it.
I own a 93 Chevy Silverado K1500 4x4 with V8 350 TBI 5.7L. so unless Chevy has changed their blocks, i would suggest that naturally your block is a SB 350. However, since your question was about horsepower, not which block you have, I will tell you the horsepower. The 1998 Vortec 5.7 liter makes 255 horsepower.
Contrary to what people think,A 1994 Extended Cab Chevy Sportside Silverado came with the 5.7-liter 210-hp V8. People think the 350's were putting out more than that but not so. this is taken from a Chevy dealership in TC..... http://www.roncarterchevrolet.com/testdrive-review.aspx?year=1994&make=Chevrolet&model=Silverado