I love my TREK 5000 WSD. I think it is really important for you to be fitted properly. I too, am 5'4", but due to my long femur bone, I fit on a 54cm. The first LBS I went to "fit" me to a 50 cm, it sounds like they fit me like your LBS fit you! Good luck!

Here is a link to several different bike fitting methods:

http://www.cyclemetrics.com/Pages/Fi..._fit_links.htm