My 89 245 did pretty much the same thing, when it aquired 278k miles on it. When the car was cold (first thing in the morning) I'd drive about 5 miles to the Interstate and it never would go into overdrive. I'd get on the interstate and drive about 3 or 4 miles and it would suddenly drop into overdrive. I did a flush and changed the filter (I hadn't done it in almost 100k), it didn't help. I changed the OD relay, it didn't help. I checked the wiring to the OD solenoid, everything was good there. Only thing left was to repalce the OD solenoid. I pulled it and just for kicks I cut the black rubber stuff off the top where the wire enters it. I found that the tiny little coil wire had broken. From what I could tell as it warmed up it would expand and make contact and the solenoid would start to function correctly. I never used the OD function and didn't have the money to buy a new one so I just "modified" it so it would stay in the OD position full time. Problem solved.
I'm sure there are other things that can cause this but the OD solenoid mod fixed mine.
Good luck,
Tony
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Tony Turner 89 Volvo 240DL 200K, 92 Jeep Cherokee 250K, 93 Jeep Grand Cherokee 213K, 89 Volvo 240Wagon 303K
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