My car wont go into overdrive

My car drives and shifts poerfect. But it wont go into overdrive or lockup. I unplugged the trans. Speed sensor and the car started shifting early and starts out in third gear unless I downshift it manually. I plugged the sensor back in, now it shifts fine except. No overdrive. The light on the dash is working. But a while back, if the shifter wasnt exactly in a certain spot, it wouldnt go into o.D. Unless I shook the gearshift back and forth a little. The light would go off and it would go into o.D. But now it doesnt.