Have a shop drop the pan, if this is possible on your vehicle, and replace the crummy fluid with new stuff. This won't get all of it -- some remains inside the torque convertor -- but it's the path of least resistance for now. If things improve, wait a few thousand miles and repeat the process. A flush will cost you more and won't necessarily give you better results.

change it and blead the system till its clear, it sounds like its been in there a very long time. if there are any metal bits in it at the bottom of the fluid I would get the transmission checked .

It sounds like your transmission is definitely slipping. If you have suitable tools you can remove the drain plug and remove the pan. If the filter is plugged it should be cleaned or replaced. Here is where the metallic bits would be, in the pan. Needles on the magnetic plug do not count. Concerning the overall condition any mechanic can test it for slipping without popping the hood.

I can tell you my fluid was black (although not burnt) and remained black after the change and yet I put 100,000 miles on it, in addition to the countless 100,000s before I got it. If it is working normally and not metal bits then have it flushed. But if it is slipping I would not invest in it.

Er.....change it?