The overdrive system consists of the input shaft, one - way clutch, planetary sun gear, ring gear, planetary carrier, overdrive clutch and overdrive brake The overdrive elements are controlled and applied through transmission valve body solenoid number two. with all these to consider, it's possible that the solenoid may be causing this shifting issue. another component that could be causing this is the Torque converter lockup solenoid if equipped. nevertheless, this task is best diagnosed by a Qualified Service Technician that has the knowlege of monitoring all the Solenoids and sensors along with hydraulic pressures to diagnose this properly.