There is a program called Backupmenu you should learn about. It allows you to back up everything about your current ststem and easily restore it. You could use Backupmenu and keep the files that would allow you to restore your current system. Then you could flash your current system and see if your gps works ok after the flash. If flashing solves the problem, you know that something about the software you have installed caused the problem. If flashing doesn't solve the problem that would imply that something about hardware or your location is causing the problem.

After you discovered the effect of flashing, you could decide whether to restore the old system or start from scratch again.