An earlier poster kind of beat me to it, but it's worth pointing out that in the 80s, the TdF winners averaged 23.1 MPH, while in the 2000s, they averaged 25 MPH. Even ignoring better roads, shorter stages, and EPO, the bike just isn't worth 5 MPH.

So the OP either got fitter, has a better position on the new bike, or never figured out how to operate the old bike correctly.