At 143,000 miles, the 722.6 transmission is hesitating in the uppermost gear change (4-5 or 5-overdrive?). The problem is consistent and no MIL is illuminated. Acceleration is still good, and the transmission feels strong through all the other gears with no slips or flares. At the last gear change, however, the RPMs drop down to 2000 and I feel a second more delayed clunk to around 1800 about a second later. There seems to be some subtle clunkiness when I let off the accelerator at the changing point. The fluid level seems OK at 80 C. What else should I check? Thanks!

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1982 300D-T (sold)
1988 300E (sold)
1994 E320 Wagon (sold)
1995 E320
1998 E300D-T
1999 E3204M Wagon
2001 E320
2005 E320 CDI