Transmission trouble

Here one for the brain!!!
I have a 94 f150 auto trans not sure of the type
but it had metric stamped on the pan and it is a overdrive
on warm days like in the summer just driving along no matter what
speed im going the trans. shift.s down to a lower gear
than back it may do this every day one or two times or 15 times
a day or one or two times a week and get this now thats winter is here
everything is fine transmission works great..
i even changed the trans. oil and filter drained tc. compleat change holds 12 quarts..
Last september i drove from north carolina to florida and back down i-95
at 80 mph it did it a few times now in town it will do it a lot of times
heres what i been told it is:
transmission bad. the TC. is bad .valve body is bad .coil pack in trans.
bad. I. switch is bad. on board computer is bad.
that can add up to big bucks to change out that stuff...
anybody have any ideals!!!! i thank you and have a good day.
Rick Midyette

Rick,

The trans is unlocking the Torque Converter because the ATF is getting too hot. It might be that the Temp sensor is not right, or your cooling system is not keeping the ATF temps low enough (very likely). Are you using Mercon V ATF, or just Mercon? You should use Mercon V.

well i will look in to that. i have a tow package
and i just replaced the t-stat and housing
and you may be right about the fluid.
think i should get a finned trans. pan???

No, it won't help enough to notice.