agreed. replace RCM. check battery cables / ground. I had that hard shift once. It felt like the car drops lower and a thunk. RCM fixed that.
if you were going into Limp Mode / Dash all lit up -- ABS Module and bleed the brake lines.

seems its never mechanical in these cars ~ it's always electrical. the car is wired like old christmas lights - one bulb goes funny and the string goes out.