Hey how are you
1- ok so fluid good no metal shavings correct ?
2- how many miles on it now ?
3- We need to have it scanned with a dealer scanner or equivalent that can communicate with TCM,Transmission control module and retrieve faults codes iff possible , you can post them back here for me .
4- what warning lights are on at this time
5- Usually if it quits suddenly , it will be more electrical, module or internal solenoids not internal clutches and requires a complete rebuild , you would have felt gradual slippage but you said happened suddenly
For now lets try a master reset ,if no scanner available to you now , let see if it is a module and we can reset it
Master reset Procedure
1- Disconect Battery Cables ( Negative & Positive Cables )you can use any electrical wire as an extension if battery cables don't reach .
2- Hold cables Together for 60 secs ,then let go
3- Wait 15 minutes
4- Make sure all doors are closed
5- Reconnect battery Cables
6- Lock & unlock the vehicles using the key from driver door side (if you have a key fob with no blade key, just lock & unlock using the key fob buttons)
7- Enter the vehicle and attempt to start
Please let me know
ASE Certified Technician