The x-drive fluid is through the dealer, or through various web retailers of BMW parts. I believe ECS has it.

For trans fluid, I would only use a fluid that actually meets the LT71141 spec, not a fluid that is advertised as being just as good as fluids that do, or 'suitable for', but which doesn't meet the spec. If you don't want to go to the dealer, VW dealers have it, as well as Esso/Exxon.

Unless you are draining the torque converter and back-flushing the heat exchanger, you are just doing a simple fluid swap. I wouldn't flush it, but I would change all the fluid that came out by removing the pan. I would absolutely change the filter at the same time, and only use an OE filter.

The above may not make any difference in your lurch, but if not you will at least have discounted the fluid as the cause of the lurch.

__________________
2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue