[Frank Miller]

When you get past 30, let up on the accelerator and listen for a thunk, what it sounds like to me, that will be the OD shifting in. Sometimes it is easier for me to hear it in second. Someone wrote earlier about driving around in 2nd OD. While that is possible it is not recommended. OD cars came with a 4.11 ratio so being a little lower you could start off in 2nd and shift to third without the clutch, and then let up on the gas to shift to OD. Depress the gas to shift out of overdrive, let up to shift in again.
If it is just not shifting out then your switch may not be addjusted properly or the grounding circuit is not working. The points need to be shorted to remove power from the input shaft to let the solenoid drop out.