Transmission fluid help

Hi can anyone help me with a question about X5 transmission fluid capacity.
I have a 2001 X5 4.4i sport with 103k. A few days ago the engine management light came on, so i took it to BMW and they came up with a problem with the output speed sensor in the transmission.
After a little investigation i decided to replace the output speed sensor + the input speed sensor + the camshaft position sensor (because i had one anyway) at my local garage. I bought a new transmission filter and gasket and some transmission flush and dropped the car off with him. The work was done and i was charged for 4ltr fluid and labour.

Now when i drive the gearbox sounds different and any harsh acceleration results in "trans failsafe" on the dash. i have only done about 15 miles like this and thought something is not right so came on here to ask. My question is how much transmission fluid does it take because i have a feeling 4ltr is not enough. Any advice would be a great help as i have parked the car up and will use my bike until i get to the bottom of this.

found this on ECS http://www.ecstuning.com/BMW-E53-X5-...ion/ES2523869/

personaly i would go with what they recommend, if i have to i would happily use BMW labeled oil = or its equivalent

I though your not supposed to change your transmission oil if the car has a lot of miles on it.

the theory behind that is the tranny is old and has worn out, the clearences have become a little bit bigger, but to conteract that the particles of shyt that has worn out is floating around in the fluid which makes it thicker....

100k should b ok to change @