My 1998 - 4R70W Tranny has 222,014 miles on it and I have maintained it since new. Oil & filter changes every 40,000 miles. It is now chattering, Banging or shifting hard into over drive. I'm not sure how to describe the feel but it feels much like if you were sitting still in netural and dropped it in drive. Only difference is it's the last shift while driving. Today I changed all 12 Qts of fluid and the filter. It seems a little better but thats all. The old fluid was almost red but not brown and the tranny case was clean. There was a little oily dust on the magnet but not much. Any suggestions would be appreciated.

 

Sounds like you have taken care of rather well,I suspect that even with the fluid/filter changes every 40K miles,the clutches are probably worn beyond limits.With that many miles on a tranny,id say its time to get it rebuilt.There of course could be some"gunk" issue in the valve body causing your problem.