2001 X5 After trans flush has shudder symptoms and torque converter not locking up

[tmv]

Did you replace the filter as well? ATF needs to be filled in between 35C-55C, IIRC. Warm up engine is too vague for that. I did it on the old 3.0 following GT1/DIS procedure. Car needs to be leveled.
1. Fill the pan until ATF drip out.
2. Close fill-plug temporarily.
3. Start engine and run through each gears, with a few second in each.
4. Measure the ATF temp.
5. Open fill-plug and pump more ATF in (when it's in correct temp range)
6. When it drip out, let it does so for at least 60 sec.
7. Close fill-plug.
8. Turn off engine.

You might not have the correct amount of ATF in there if you didn't fill it at the correct temp. More or less than correct amount is NOT good.