rear wheels locked up while backing down a grade

I put it in drive and was able to get back up to the level parking area of my driveway but now it won't move backwards at all in reverse or neutral. It's cold now and I started it up and could feel it go into reverse but it wouldn't move and it stalled. I tried pushing it forward and it seemed able to rock forward like when you are hand pushing a car and you have to rock it forward and back before you can get it moving. It started to rock forward but not back. The tranny fluid looks light brown and thin, after I got fluid, filter, and pan gasket service about 2 months ago. I've had the car for 8 months and put 17,000 miles on it in that time. I don't use the parking brake so I'm really having a hard time trying to imagine what could be causing this problem. I would really appreciate hearing from anyone who knows what this is.


For more details : explainer video

Did you jack up the rear end and can you turn the wheels by hand backwards?