I have same year and same engine car and exactly the same problem. I have changed filter and oil, but it didn't help. It actually became slightly worse. The oil was black and magnets full of fine metal particles. When you change oil, you actually change just a half of it, as a lot of oil (about 4 litres) stays in torque converter and radiator. Anyway, for now I have bought Lucas oil transmission fix. Didn't put it in yet, but I will. I think previous owner used it already and it explains why slipping got worse after oil change. In any case, these are not good symptoms you/I have. Dark oil means wrong pressure and fluid overheat and this means you need to repair your torque converter and of course, if you remove your transmission from the car, it make sense to check the gearbox for worn friction discs etc. I have tried all sort of scanners and no errors. I wonder if Transmission ECU actually responds. I'm mentally preparing myself for transmission removal and reconditioning it in my garage as DIY project. To give it to professionals will simply cost more than a car (around 2 th.). Luckily, this is very simple and popular gearbox, which have been used on many cars and very long time (41TE, A604). If you will type it in google, you will find plenty of info. I'm not recommending to go with e-bay second hand transmissions as it is very low probability to get a good one. These transmissions need frequent fluid change and many owners doesn't know that and therefore the average lifetime of this transmission is 100K. I hope it helps. Sergejs.