I read this on CNET:
The reason that the system has to memorize maps in this way is not immediately apparent, but after a chat with a Pioneer technician (our test unit is so new that it didn't come with a user manual), we discovered our major gripe with the Avic-D3. To wit, the relevant DVD-ROM (there is one for the western United States and one for the eastern states) has to be inserted into the disc slot for the unit to make route calculations and to display maps on any level of zoom closer than the 25-mile scale. When the DVD-ROM is removed--for the purposes of using the disc slot to play CDs, for example--the Avic-D3 resorts to "memory navi mode," which will allow drivers only to access the last route that was entered. Memory navi mode also disables destination entry and any editing of the current route. Accordingly, users of the Avic-D3 will have to ensure that they always have the relevant disc on hand each time they want to enter a new destination or add in a waypoint to an existing route. Alternatively, they could leave the navigation disc in the unit and resolve never to play a media disc.

 

why dont you look in to the kenwood dnx7100..they can be had for less than the pioneer avic z2.plus its has a hard drive built in.

 

I was looking at the D3 and the Z2 and I ended up going with the Avi-205 with the Blackbird unit. I love it. The blackbird has a built in MP3 player and Bluetooth and a place for a SD card. I have my Onstar and my Wheel controls working. I just ordered a USB interface. You can plug USB memory into it with lots of songs. I ordered a compact 120 gig external HD that Im gonna use on it with all my CDs and some Movies and such. It works through the CD Changer port on the back.

This is a much better unit than I thought it would be when I was looking to begin with.

 

I am shopping around. I looked at that unit, there was something I didn't like about it. Just don't remember what. .

 

I am going to install a navi head unit in my '05 GMC in the near future also. For what it's worth, I have two vehicles with navi radios right now. In one I have an AVIC-N1, in the other I have an Eclipse (at work right now, can't remember the model number). Obviously the N1 is a single din while the Eclipse is a double. As stated previously once you set a route with the Pioneer and then remove the disc you lose quite a bit of features versus having the nav disc inserted. On the other hand, the Eclipse has double slots: one for audio cd's and one for nav or movies. However, it does cost more. Mine was already installed when I bought the vehicle so I can't help with any install issues (TBSS, should be similar to the trucks) and the AVIC was installed in a non-GM vehicle, but I still might could help with any problems should they arise. Also, you might want to check out Diesel World magazine's October issue because they install the Pioneer in a GM truck. I do custom stereo work on the side and again if you run into any problems (should you do the work yourself) I would be glad to help!

 

We have the Avic N1, no problems. Recently the S2 for me at Christmas so I didn't have to replace my head unit.