I have a '91 560 SEL with 70k (wife's trailer queen) and a '91 420 SEL with 191k which is very well maintained and used daily about 100 a day. On the 420, I notice that the trans may not be downshifting from 4th to 3rd or 3rd to 2nd as the car slows down. This leaves me in too high a gear for proper acceleration. If it comes to a stop, it will properly downshift for a 2nd gear start. It upshifts fine, and manually shifts fine. Trans has been well maintained with fluid and filter changed every 2 years. Engine seems fine in all other aspects and gets between 16 - 21 mpg. Any suggestions on what to look for or test?

Thanks