Auto box?

[Toy car guy]

Hi Guys, just picked up a 2004 2.5 V6 Mondeo with an auto gearbox, really nice car, but finding a couple of glitches with the box. Firstly, are the gear changes in these boxes management system controlled or speed controlled???

What the box seems to be doing is momentarily slipping out of gear when cruising on a long(ish) run. and on slow speed descent of hills, the box is changing down to a low gear giving a noticeable engine braking effect, but then having to change back up two gears as soon as you touch the throttle. I'm thinking it could be in need of a fluid change maybe??? Or is there a system reset on these cars???    

[pragmatix]

At very least a fluid change, what's the service history, do you know anything about it