AFAIK, as of 2012, the Trek 4000 series and 6000 series used the exact same frame (Alpha Gold aluminum). The difference was in the components. By 2013, the 6000 series was no more, and only the 4000 series remained. LBS is correct, it's the same quality frame (actually, more than likely it's a nicer frame than you had, for the reasons mentioned by jimc101.