MB specifically says to DISable the Gravity correction when you're using Edge 305/705 (with barometric altimeter). What happens when you enable the autocorrection but disable Gravity (looks like the one thing you didn't try)?

Also, what level of smoothing do you use in SportTracks? I have mine off for elevation, off for cadence, on at 3 (of 150) for speed, on at 10 for HR. I think I'm going to increase the HR smoothing, but it seems to work pretty well for speed - just eliminates the obvious spikes and not the momentary fast descents.

SportTracks worked so well to correct distance when I was having that software bug, that I'm inclined to trust its elevation data as well (with smoothing off, especially important in my terrain of short, steep hills).