If you are hour building for CPL I would forget the GPS, use basic Nav but also use VOR/DME/ADF (actually not sure if ADF is still needed), i.e. The things you will be using on test, and make sure you are really comfortable with how to use them for tracking and position fixing. I would also suggest doing a few flights where you practice all the general handling you will need for the test so make sure you are completely happy with stalling, steep turns PFLs etc. and then do a few circuits with different approaches at the end of the flight.
