Same Route: LARGE difference in elevation gain. What the heck?

My cross country coach ran this route back in 2010: he had 1027 ft in elevation gain over a 7.57 mile run. http://connect.garmin.com/activity/41400397
I ran almost exactly the same route last sunday, except I made it an 8.5 mile run by going around the longer side of the lake in the beginning. But the elevation gain was MUCH MUCH different - 588 ft. http://connect.garmin.com/activity/325596240

Four hundred and thirty-nine freaking feet apart. What. The. Hell.

Now if you notice, the lowest and highest elevation only vary by 1ft which is pretty accurate but its the elevation gain that's astounding. I'm just extremely confused right now to what could have caused this.

You're using a device that doesn't have a barometric altimeter, so Garmin Connect (not your Forerunner) is using it's own internal idea of elevation. From my experience, that's usually pretty accurate, although there are some interesting quirks in Garmin Connect's maps in this area (central PA). Your coach is using a device that must have a barometric altimeter, because note that Garmin Connect says "elevation corrections disabled". Have him turn on corrections in Garmin Connect and see what happens. Although Garmin claims that its devices with barometric altimeters are more accurate than using GPS elevation, I've seen some pretty big deviations. Once my Edge 705 lost 500 feet from the beginning to the end of a loop (start and finish at the same point).