Just a thought on U/D pullies.....If I did pullies again, I'd go with steel March pullies. I had the ASP pullies on mine and I could tell a difference in throttle response as well as some gains by the SOTP dyno. But...the aluminum housing sucks for durability. Mine was stretched out enough that I couldn't keep my crank bolt tight. It might have survived if I had followed the torqueing procedures but I just put an impact on it and tightened the $hit out of it. It lasted about three cycles before I figured out why I couldn't keep the bolt tight. Fortunately, I didn't gall the nose of my crank and was able to put the stock pulley back on.
I had to do ASP at the time because March didn't do U/Ds for the 5.3
'02 Silverado Z-71, STS Turbo @ 10psi, TRT Custom FMIC, Comp 222/218/115 cam, Patriot Gold Dual Springs, Hardened Push Rods, 60# injectors, 160 Thermo, FAL E-Fans, Nelson Harness, Yank 2600, Built Rock On VacMod 60E Transmission,Walbro 255 fuel pump, ASP Underdrive pulleys, Gibson Shorty Headers all polished up with a Nelson Street Tune