did you get the p1 package and then replace the gps or no p1 package at all?

 

The P1 package is a must as far as I can tell...Parktronic and the mirror features, entertainment system and power tail gate, etc + navigation.

Why would you think you need to replace the nav system? I had a similar system in my '06 S430 and never had a problem getting anywhere. True the maps lack some detail in certain areas but once you learn the routine, especially by voice instructions it is fine. I do not anticipate any problems with the navi in the GL when I get mine in April.