1984300sd Transmission Question

[jack avant]

The transmission will not come out of overdrive at times. The first time I was passing a car, and noticed it would not shift back to overdrive. If I start off from the stop position it will change fine about 50% of the time. I have checked the switch under the fuel pedal and even unplugged it, but that did not help. Will the transmission kickdown solenoid cause this problem. Help needed bad!!!