I have a 2004 Volvo S60 2.5t awd, auto trans (unfortunately but it was cheap and didn't take much to become a very sweet safe vechicle)

I was coming home from work one morning, and upon pulling away from a stop sign, I got about 3 feet and started rolling backwards... Everything including park became neutral (transmission itself does seem to be engaging). Trans fluid is nice an clean does not smell nice red color. Linkage is working. I can reach under the car and spin the rear driveshaft by hand without much effort. When you put it in park, well attempt to anyways it makes a terrible grinding sound as If you were still driving an slammed it in park. I know these have many many transmission issues although prior to this it shifted like butter, never flared up or any of the typical Volvo trans issues like my prior 02 s60 had. I'm just stumped, I'm thinking transfer case or something between the trans and transfer case. Have not been able to get it onto a lift as my trusted mechanic is dealing with a lot family issues an such so he's away from his shop. I got this s60 for a winter vechicle to get to work at night in the sometimes semi harsh pa winters as my fwd s60 was amazing in snow so I can only assume awd will do even better. For some silly reason I have a love for these goofy cars despite their gremlins. I have under $1000 invested into it so far so I don't mind forking out to fix it, if I can figure out the issue. Just put some suspension work into it, was about to do brake upgrades all around too.