So I found this thread in google after having some issues. I have a 2007 Escalade (Late 2006 manufacture date) with factory nav and the rear entertainment option from the factory. I have been having some issues with the GMX550 formware revision 1.4z. First off I put in a GMX322 right after I bought the truck and it worked flawlessly for the 2 years I had it installed. I never even experienced the nav tracking issues after DVD in motion. The worst it ever was would be about a mile off and it would snap back to my current location in a few seconds. I have been dying for on screen iPod control and when I saw the GMX550, I figured the upgrade would be worth it, and since I never had any problems with the GMX322, I didnt hesitate to upgrade. Needless to say, I am second guessing this decision now. The sound out of the iPod dock connector is horrible. I have tried every EQ setting available on the iPod and my radio and it crackles with any bass at all even at low volume. The entire stereo is completely stock by the way. With CD audio, XM, and radio it sounds great. I drove to work this morning and everything was fine. Getting in the truck after work, the radio wouldnt turn on. A few back and forth turns of the key and I finally got it to power up. Pulling out of the parking lot, the OnStar icon came on the screen and the radio went silent then started to feedback horribly. (I have never activated the OnStar in the time I have had the truck) The next thing I hear is the lady asking for a number to dial. Hitting the phone button on the mirror to hang up and right away it came on again. It proceeded to sporatically do this all the way home. All Lockpick features were off during this time. I got home and got out of the car and the radio went back into OnStar and would not turn off with the key out and door open. I finally got it to turn off and armed the alarm and went inside. I came back out 30 minutes later and the radio display was on again. I pulled the lockpick out and looked at all the harnesses for frayed wires but found nothing. I put the GMX322 back in and all is back to normal. I will be calling Coastal Tech tomorrow to see if they have any answers about the erratic behavior and the iPod sound quality.
Sorry for the long winded first post, but I am looking for any answers at this point as well as to share my experience with anyone looking at this unit. Hopefully they get the bugs ironed out with a firmware update soon. If not I am hoping for a refund and sticking with the less feature rich but stable device.