94 explorer transmission

At times, my 94 Explorer with 75000 miles will shift out of overdrive and not go back in. Usually when it is cold, it goes in OD and will do fine for about 5-10 miles of highway/interstate driving. Then it will shift down out of overdrive and won't go back in until I let it set overnight. Transmission fluid exchange and filter done about 10k miles ago. The problem just started and is sporadic. Usually not a problem when driving less than 15-20 miles. After driving at highway speed for 10 -15 minutes the problem usually occurs. Otherwise, transmission operation is perfect. Please help.

Since this post, it now does not go into overdrive at all, even when I first start out in the morning.

I read somewhere that voltage problems can cause a/t issues. Apparently the explorer o/d is controlled by voltage and any change in voltage might cause the tranny to change gears. Take a look at your alternator/regulator. This is a ripe age if you've still got the original alternator in there. It might not be apparent due to variances in operating temperature, driving conditions, etc. But it's a start. Also be sure and check out all your wiring harnesses. It can also be caused by poor connections, intermittent shorting, etc. Pay particular attention to those harnesses that come close to any exhaust pipes. Hope this helps. Good luck.

Probably the TCC(torque converter clutch) is unlocking. TCC can "feel" like a shift, but it really isn't considerd a shift. Its always the first thing to show symptoms when there is an electrical problem. Someone needs to monitor computer data stream on the TPS, TCC, MAP and more. With a scan tool...

theres some transmission control soleniods in the valve body . it is a task , i recommend having a trans specialist take a look at it.