It maybe a governor issue. They will sometimes go bad and the first signs of the governor going bad is that your vehicle transmission may hesitate when the gears are shifting.
A lack of fluid, or just a general slip. I'd check the fluid levels first and then if that is not the problem, have a technician look at the transmission.
The most common cause is low levels of transmission fluid, or old/used up/contaminated fluid. A flush and refill of the system should clear it up. Otherwise, it might be simply wearing out, at which time it will need a more involved service.
Low transmission fluid is the most common problem in hesitating transmissions. When fluid levels get too low, transmissions often begin to hesitate or slip.
There might be a problem in you transmission. You might have low oil level or old oil in it. Try changing the oil, if it does not work then contact a local workshop.
Transmission hesitation can be caused by low fluid levels, bad trans filter, high rpm's, fluid leak, hard shifts, loss of acceleration, worn bands, worn gears, or a bad torque converter.
There are a few different causes for the reason that your Ranger's automatic transmission is hesitating. One cause could be transmission fluid, check the level and quality of the fluid.
could be as easy as low fluid, have you done a transmission flush or service on it yet? If not do so and you will be able to see a little better whats going on