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Ford they have a secret?

92 Explorer/ auto trans shifts after a 10 min.warm up, runs fine all day. But tomorrow requires a warm up again. Fluid is fresh. Am I overlooking a sensor or somthing?

No this is unlikely to be a sensor. Have a transmission technician connect a pressure gauge to the line pressure tap when this problem is likely to appear (after overnight cool down). I suspect you/he will see very low pressure until a leaking piston seal starts working. This is usually termed a ‘lazy piston seal’ that has gotten so worn and hard that it will not seal until the fluid warms it up and it is able to seal against its sliding surface. Sadly, you are probably looking at a overhaul.

BTW how many miles on this 17(?) year old transmission.

Ford transmissions usually need a rebuild when that happens. It’s no secret.

Classic symptoms of hardened clutch piston seals. This happens with age and mileage. The piston seals harden then leak when that clutch is applied. As the trans warms up the seals soften and will not leak as much. You can pour a can of Berrymans Chemtool in the trans. If it is indeed the piston seals leaking, this will tell you for sure and it will soften the seals to where it will shift normally.