Hi Grasstrip,
I was in a very similar situation to you in February. I had passed my PPL and wanted to get in some flying. Even though I knew my nav was fairly good, I wanted a little bit of re-assurance and bought a Pilot III.
I learnt how to use it before I went flying and booked an hour with an instructor. We disappeared off for an hour and did some PFLs and then spent 20 mins looking at the GPS. This meant I had then added safety of being able to arse around with the GPS whilst instructor helped with the lookout.
I still plan my flights as if I were training and fly DR with the GPS for backup, and it does make me feel happier.
If you still have to fly a couple more hours with an instructor anyway, buy a GPS and go up and have a play, while he acts as "safety" pilot. That way you know how to use it when your up solo, without having to flick through the manual.
Just my 2ps worth.
F - Wyg