1997 Ranger 4.0l will probably have a 5R55E 5-speed trans, but..............
Some did still have the 4R55E 4-speed
Depends on the assembly plant they were made at.
If you look at the drivers door label find the TRANS code letter, bottom of label
T = 4R
D = 5R
Yes, just drain replace filter and refill.
If you are having any problem, flushing won't help and may hurt, if you are not having problems then flushing "might be OK" but won't help much.
Engine oil and trans oil flushing were "invented" by shops because they are profitable and fairly safe to do, since if a problem occurs they can say it was a pre-existing condition, the flush just found it for you, "thank goodness it didn't strand you somewhere", lol.
Check old filter for debris