I got mine from Brian at BD Turnkey and from the information he has put out, Chevy only made them for a few years, so not very common. They came in the higher end GM and GMC trucks from 2005 to 2007 and only 10 to 15% of those. The L33 version has the all aluminum block which is 80 lbs lighter than the cast block and has LS6 heads and flat top pistons, which is why they call it the High Output. I was just lucky that Brian had one come in when I was looking. He states on his website that he can take the LM7 version of the 5.3 and add a hotter cam and get get close to the 350 hp. Maybe an option...