1999 540i Auto Trans fluid black and Burnt/ Help?

[540EyeHer]

So my540i/Auto has 185K on it, And I have had it since 134K, never checked the Trans fluid. Trans was hanging up in a lower gear on a grade, otherwise works fine. Checked for Trans codes, and showed code 31 (slipping I think). So I take the car to my mechanic, and he checks the fluid, and it's full, but black and burnt. My main question is, at this point do I still spend the money to change the Fluid/Filter, or do I just leave it alone. Has anyone had a Trans fluid looking like this on these cars, but the Trans still worked for several years? Thanks.

[BimmrMeUpSnotty]

Change it out, filter and all. A change will not get all the old oil out, put a few thousand miles on it, then do another flush and fill, you change it all out at one time, that will shock the system with too much of a change, this is when transmissions freak out, and start tossing all kinds of issues.