You're video is private, but if you get an RPM surge under a load then likely the TCC is dying. My 00 GT has been doing this for a few years now and I've been babying it along so far. I turn off my traction control which seems to help it some but I can still make it do it when I get on it hard enough. I also just drive around in 3rd and manually shift it into OD when I'm going to be above 50mph for a while, otherwise it just hunts around and I hate the excess shifting.
Granted I have a high mileage trans. but it started out just like yours and now it'll slip/bang in first if I jump on it from a stop and it will slip on a hard downshift too. It's just time for a whole rebuild at this point for me. You may be able to extend the life of yours with a Trans-Go shift kit and filter/pan drop fluid change. I've been running the kit in mine when it started acting weird and it's still going. And no, I didn't do the whole kit just the 1-2 and 2-3 accumulators. Didn't touch the rest.
