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.