I think Ford says at 200K to go buy a new one. LOL
You will be able to tell the trans fluid by looking at it.
Get a white paper towel and a white piece of laminated paper. I use the white information sticker under the hood and wipe the stick on it.
150K never been changed fluid will look it.
It will be dark and should have brown tones to it if not darker.
If it has been serviced it will be much lighter or at least deep red mahogany looking and smell better than brown burnt stuff.
I would never flush any trans. I refuse to give up pan drop and cleaning all the grit in bottom of pan and getting a new filter for the convenience of the shop doing the work?
I also never do flushes on high mile trans unless they have been serviced a lot and often.
I love the pre 03 ones with drain plug on converter.
So figure out trans then do as others said about maybe plugs or pull one to look at them if you don't know history.
You should check all to make sure they are tight. Plugs like to loosen up and blow out.
If you have all oem coils you really don't need to replace until one misfires.
If you have a shuddering, had to see if it's ignition miss or converter shudder.
Get a scan tool on it and read the cylinder misfire counts then clear codes and drive it a round then read them again.
If unknown history, unless plugs look relatively new, I would put new motorcraft platinum plugs and new rubber coil boots in.
Look for any badly deteriorating vacuum lines at pcv and change pcv and back of intake problem areas.
Change front and rear diff fluid and transfer case if no history of it being done.
Check spare tire for air and make sure mounting lowering works freely. Make sure it has a jack and tire tool and jack raising handle.
Clean throttle body inside and butterfly plate with rag or toothbrush and cleaner. Supposed to use special spray but ask me if I always do this and if any special coating has ever come off....
Clean MAF sensor wires with MAF spray. I use q-tips too but you're not supposed to. I'm such bad person. How do my cars ever get me anywhere???
New air filter K&N and cut out side of box if you want to try to increase mpg. It was noticeable in my 98 Durango 5.2. Never tried my wife's 2000 Exp- she pays for the gas in it.
Oil change, maybe high mileage Mobil 1 5w-30 or 10w-30, but I would pass on 5w-20.
Motorcraft oil filters best cost effectiveness at Walmart or better filter. But never orange Fram. I just use Motorcraft FL-820s. Don't need any better and price is great.
Keep and eye on radiator hoses for age, swelling, cracking.
See what coolant looks like. If not good....or if not green in my case I hate the extended crap and put green back in everything. You could dump from lower hose and refill, run and repeat a couple of times.
Thermostat if original is getting weak and by now and not giving hot heater and warming up as fast.
Pop the therm off at top hose and good time to flush water through. Then 50/50 with green coolant.