Hi there, new to this site, have a question, I am looking into buying a used 2006 Silverado, The research I have read indicates to me that the L33 Aluminum is significantly a better motor than the cast Iron. Anyone agree / dis agree. Also, I though in 2005 all motors were l33, well I just looked at a 2006 and it was cast iron. This dealer is really pussing this 2006 cast iron on me. thanks