Out of gear

2000 Ford Contour (automatic)

When I’m driving the car it seems like it does not like to stay in one gear and jumps around. This only happens after the car has warmed up and had been driving for little while. It happens at lower speeds and higher speeds, especially on the interstate. I can be going along fine for awhile and then all of a sudden, it wants to down shift and at times it doesn’t to stay in 4th gear. As I slow down it still wants to downshift. I thought it may be the fuel filter, injectors… but the more I look at it, could it be transmission regulator/sensor???

When was the last time the transmission was serviced?

And, is the check engine light on or the O/D off light flashing?
Also, how many miles?
Has the transmission fluid level been checked?

And, is the check engine light on or the O/D off light flashing? no, no
Also, how many miles? 258,000
Has the transmission fluid level been checked? serviced about 20k miles ago