Does the speed of the car make a difference in the shudder? Temperature a factor?
Flush the transmission. It may help. Sounds like the 3rd or 4th clutch is going or it could be a sticking valve or solenoid. If you catch it early enough and its a sticking valve or solenoid, it may correct it before it damages the clutches too much.
With mine, the adaptive shifting programmed in the TCM was covering up a problem with 3rd clutch until it was too late. Had to rebuild it again after 17k miles.
You may consider removing the pan for inspection and cleaning the sump screen.