Could you please tell me where (on the tranny?) is this overdrive switch?
I am having a similar but different problem as "wacky overdrive". My 740 will not willingly go into OD. It goes into od when it's good and ready. This can vary from 10 or 15 minutes to an hour or more of driving! (this can be awfully slow going and makes highway travel hazardous or gas guzzling expensive) When it finally does drop into OD everything works perfectly well including the OD selenoid switch for up and down shifting. All the gears shift and mesh smoothly. I too have flushed, checked the kick down cable, replaced the od selenoid 6 mths ago, replaced the harness and plug to the speed sensor (which gave me my speedo back) that went a few weeks ago... but no proper OD. I suspect that there is an electrical problem somewhere.
I've heard of a locked up control valve (torque converter?), a throttle position sensor and now an overdrive switch?

Can you or anyone direct me to the actual location of these components (or at least the od switch) so that I can check for bad connections/wires etc. ??