Robert J Heintz

I work for a Chevrolet dealer doing dealer trades, so I drive a lot of different vehicles and know which options I like. I have noticed some silverado's seem to be quicker that others, they all have same 5.3 engine, 8 speed trans and 3.23 rear ratio. All are crew or double cabs, standard or short beds. the only difference is some have Z71 package and others just 4 x 4. Anybody h ave any ideas what the difference might be? Thanks Robert