Rocker Arms or Underdrive pulley?

I have a 2005 chevy silverardo with the 4.8. Right now i have my muffler cut of but left the cats on, and i have a spectre CAI. I plan to buy a hypertech power programmer iii soon because i can get it for pretty cheap. I am looking to either get rocker arms at 1.8 and replacing the springs with it(only if its highly recomended), or doing a new pulley set-up. Which is more worth the money and work, and where can i find a pulley set-up with an alt and belt included?