I’m having the same issue as the OP. So I got the p770 code, and drive it for a few days and cleared it a few times. Then, one day, I went to leave for class and the car wouldn’t move. I could put it in drive and reverse, but it wouldn’t go anywhere. It eventually got to a point that, if I put it in drive, it would sit for like 30seconds and then slowly creep forward, and I could build momentum up to get it to move. Reverse worked a little better than forward, but it wouldn’t still need to sit for a few seconds in gear before it would move. Isearched the forums and decided to replace the solenoids. I completed that 2 days ago. However, now the car doesn’t move at all.
The fluid was very dark and smelled bad, but it’s got 260k miles and I’m pretty sure the PO didn’t ever replace the fluid. I cleaned the pan and everything before I put it back. I didn’t FLUSH all the fluid, I just added the 4qt that came out. There WERE fragments in the oil pan, but they were plastic, not metal. I figured out that the plugs on the solenoids had become so fragile that the plastic part of the plugs broke into like 15 pieces. I took the metal interior of the plug and slipped it onto the solenoid so that it was very tight.