NAV not working after iPod install???

[JKWH2SUT]

I recently had an iPod adapter installed so that I could play my iPod through the OEM Navigation in my 2006 SUT. After the install, the NAV read that I was in a totally different area of the country than where I was actually located. After a few hours, it finally found where I was, but now it intermittantly starts thinking I am on different roads, etc.

Can anyone explain why it is doing this? I had the iPod installed at a Best Buy (which was probably my first mistake), but they had to take out the XM radio module in order to install the iPod adapter module. Now the NAV isn't working correctly all of the time. Yes, I am going to call them back, but would prefer not to deal with them any longer if I don't have to. Any suggestions?