I also think its the GPS. I was using SFL and everytime it was searching it would just reboot. Tried again and behold it would reboot. It did it atleast 4 to 6 times in a row. I also have this app called SpeedView installed and it uses GPS. The second that I tap it, Well you guessed it. It reboots. I have updated to Froyo and still the same deal. My wifes Evo has never experienced this untill today! I asked her when did she last use her GPS and she replied about 5hrs ago. We where in the middle of a convo when it just rebooted. Her Evo is stock.
Hope some one will come up with a solution.