Assuming it has never been swapped out with something else, you probably have an FM-132. What you have is sort of interchangeable with other years but the physical length of the thing is the main point. What you have now is really the best thing available in your model year, nothing else is better and nothing else is a plug and play swap.
That said, the M5OD is a significant upgrade but it's longer so you would need the correct length driveshaft. Shortening the one you have now is the easiest option but you could find one from a 1st gen long box automatic - Ranger GTs were all long boxes IIRC and the auto would be the same length as an M5OD. Trucks newer than 1990 or so have larger rear u-joint flanges so you cannot use their driveshaft without running into issues at the rear axle.