katluvr, I'm new to using a Garmin, and I've noticed a difference too. Not as dramatic a difference, but I was just using an online map to figure distances, after running. The Garmin figures it slightly shorter, more like 5.0 to 5.15. I trust the Garmin more-- it's proven accurate on the track.

Today was a cranky run, body and mind alike. Only went 3 miles or so. But a dramatic cold front's coming today, and I'll be needing to break out cool weather running gear this weekend. It could get down below 40F! I'm so excited! Now I need to remember where I put the mittens and hats.