300 SEL Transmission Downshift Trouble
It's a 1990 with around 185k miles. Fluid/filter hve about 20k miles over two years.
Wife reports that when highway cruising, if the accelerator is let up, transmission downshifts to third and will not go back up into fourth when accelerator is depressed. If the car is stopped, it will upshift properly again.
This problem started two days ago, and wife reported that it did not do it this morning. Commute to work is about 20 miles, so that's plenty time to get up to temp. Unfortunately, we couldn't swap cars today so I haven't had a chance to drive it myself.
Suggested places to start and things to look for?