I have a 2003 silverado with the 5.3. looking to buy a used hypertech power programmer, anyone else used one of these? how much horsepower gain should i get?

 

None, change your shift points and your speedo. That's prolly it. Programmers aren't worth the hype they get from businesses. Think about it. Programmers are boxed tunes, designed to work on every truck they're made for, but is every truck goin to drive/act the same when you change parameters on it? Look into custom tunes from
Blackbear performance, gowheatley.com, or a local dyno/street tuner who has a good following. Typically 25/25 hp /tq gains and that's just the tune. Add things like Longtube headers and cold air intake you should see another 20 on top of that