Transmission sometimes don't shift
 

Pardon my bad grammar, but my '87 300TD wagon is sometimes acting up. The great majority of the time the transmission operates as intended. Shifts are timely and appropriately seamless or firm, depending upon throttle position.

However, every once in a while it is very reluctant to shift up. It will hold 1st gear until 3500 RPM, then hold 2nd until 4500 RPM. As long as the transmission does not make it out of 2nd gear it will behave like this. Come to a stop and you get 1st gear for a long time, then into 2nd.

Once the tranmission shifts into 3rd - about 50MPH road speed regardless of throttle position - it always behaves normally from that point onward.

This first happened about a year ago, then two weeks ago, and then yesterday. Today I rode my bicycle to the office, so it didn't happen. :)

The car (and trans) have about 135K miles. Service has been by the book, with full fluid and filter changes at 30K intervals.

Has anyone seen this behavior before? Any thoughts on the matter?

- JimY