Never had the problem but can give you places to look from FSM troubleshooting section (D range Test).

Problem: Will not upshift 3-4 speed with throttle valve opening under 85%

:3-4 shift valve malfunction
:Governor malfunction
:OD OFF switch or OD solenoid malfunction

Does the OD OFF light work? I don't think the "D" light is connected to the problem, may be just bulb. The FSM is not very good at explaining tranmission and location/testing of components. It does not say if OD solenoid is accessable from outside of trans. The OD switch circuit is normally closed so a break in the circuit will prevent going into OD. I would first try to trace OD switch circuit.