I've had my Garmin 645 (no music) since July. Within the last month, the GPS has been way off. 5 miles into my 22 mile run last week, I went from an 8:20 pace to a 6:45 pace to a 6:30 pace to a 12:00 min pace to a 16 min pace, etc. Super frustrating! I have had Garmin watches for over a decade, so I know these things happen, but this is happening every single run. I've tried updating the watch and resetting. Nothing seems to work. Anyone else experiencing these same issues? Any recommendations on how to fix this? Thank you!