I just wanted to let everyone know about an issue I just found out. I put 5% tint on my 2007 Denali on all windows and on the front windshield I did 50%. 3M Ceramic Tint states that their tint doesn't contain metallic elements so it won't interfere with GPS signal or radio. Well that is incorrect. My vehicle has the Navi built in and a few days after the tint was put in, I lost GPS Signal. The dealer swapped radios, as well as installing a new GPS antenna. After exhausting all options, they asked for me to get the front windshield tint removed to see if it was the problem. I had it removed today and once again I have a GPS signal. The GPS antenna is mounted beneath the center of the dash. So I plan to contact 3M regarding this issue. I had to pay $99 for the install and then $40 to get it removed. Just a heads up for everyone.