Anyone having problems with their GPS? The first day I got the phone, the GPS worked wonderfully and got a great signal. Three days later, driving down the same highway, the signal was spotty at best and the little dot would often move far off the freeway then back on or jump all over the place. This has happened two days in a row. Now, this could just be normal GPS behavior, as I've never owned a GPS unit. Anyone have any insight? Is there a problem or are these things just quirky for a few days then they work again?