There are sporadic reports of the Ipad overheating and shutting down, but these are countered by reports from other users of running the Ipad in sunlight and getting it hot and it kept going.
So it may be dependent on the backlight brighness setting, which would be fully expected as practically every other "high power" tablet computer implements similar brightness-related power management.
I have found the GPS in my Ipad2 to be so unreliable it is all but useless - this is in the TB20GT cockpit which has a composite roof. The only way to make it run was to use the XGPS150 external bluetooth-connected GPS.