I'll have to pay special attention to what is happening to the rpms. Normally I try to keep my eyes on the road, but I'll check next time. If I keep going WOT until 9000 rpms in 2nd and shift the 3rd, I no longer have the rev hang.

 

Two videos:

http://www.youtube.com/watch?v=IhT1evrOx24
That's in 6th gear, throttle floored

http://www.youtube.com/watch?v=c8ctEWFklG4

 

are you getting all the way off the clutch pedal on the 1st-2nd shift? the transition is going to be slightly different than 2nd-3rd and 3rd-4th shifts.

 

I'm all the way off the clutch.

 

that second video is exactly what i saw in my car. and from your first video, it seems that you're fine in 6th gear, which means you're not slipping much at all. for my car, i started slipping from 1st to 2nd, then from 2nd to 3rd, and so on. THEN, one day, it slipped in 6th on the highway as i tried to pass someone. if you start getting the rev hang in your 2nd to 3rd shift and so forth, then you might need to look into a new clutch. it'll still be driveable (for a while), but you just can't get on it hard, especially in 5th or 6th gear.