Welcome to The Ranger Station!
Many Rangers came factory with 16" wheels, like my 2000 4wd did, 245-75-16. I replaced those with 235/75-15 for more power and quicker acceleration. I use a speedo correction chart and my ScangageII to compensate for the speedo error.
My other 2000 (2.5 2wd, manual) had 225/70-15 and I put 245/65-16 on it and made it handle a bit better, but I could feel the extra unsprung weight. It rode better with the bigger meats but mpg dropped.
Speedo correction is covered well in the Tech Library (tab at the top of the page). It can be problematic with automatic transmissions (shift points change) and ABS.
What size tire is a frequent question with many answers. Knowing
what you have now may help others help you decide, so take the time to fill out your truck's details.
My 3.0 engine, driving 4.10 gears on the bigger stock tires lacked power to me, especially up hills. If yours has the 4.0 engine, lack of engine power is less likely, although gears do make a difference. 4.10 and 3.73 are pretty common. If you have lower than those, you might not want really tall tires (>30").
MAKE SURE that the wheels you buy have the same size center hole and backspacing. Ranger wheels are hub-centric, meaning that center hole MATTERS. Some years had manual hubs and I don't know which had smaller center holes.
http://www.therangerstation.com/tech_library/TireFitment.html
http://www.therangerstation.com/tech_library/wheel_fitment.html