Chrysler Voyager Transmission

My Chrysler Voyager 1994 3.0 automatic transmission is changing up gears too high, 1-2 @ 40 kph 2-3 @ 80 kph no idea if it has an overdrive, i think it does. I have been advised to try changing the oil and filter, but after reading about it, it says to adj the bands, would that give the symptom of high revs gear change. If so would you recomend a dealer to do this adjustment?

If it is a overdrive I would check for codes first.
Get it on a good trans capable scanner and check it.
Post back code no.
MT