Transmission issues 2004 X5 4.4

[jlanzone]

I have a 2004 X5 4.4 and I just went off of CPO with 100,00 miles. For about the last 15,000 miles I have been having issues with rough shifts both up and down from 1 to 2 with the automatic, particularly when the car is cold. It seems to be getting worse as the miles pile up on the car. The great majority of the miles have been highway driven. I have had it evaluated by the dealership about three times while the car was under warranty and they said there was nothing wrong. I had done a search on this forum and someone suggested a transmission fluid and filter change but the BMW mechanic/adviser recommended against it and did not do it despite my request that it be done. it is the original fluid. My guess is that I will have a catastrophic tranny failure withing the next 20K miles now that it is off warranty. My question is this: How much is a new transmission for a X5 4.4, both new and rebuilt? I am looking at ballpark figure. My service adviser said that he recently replaced the transmission in a 750iL and it was $8K ! My second question is how many of you would trade this car in at this point while it is still running before ? The car otherwise is in pretty good shape and meets my needs well. Any ideas appreciated.