The overdrive lock out light is staying on, the button on the shifter
gives no response. This was at first intemittent, sometimes when
started the light was on, sometimes off. Now it is always on and the
car won't shift into overdrive. Most of the driving is in town, and I
have let it go, now I need it for a highway trip. What is causing
this?

Will driving it on the highway in 3rd (?) gear at 3500 rpms be bad for
it?

Thanks