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You can try the search function as there have been a few questions on this recently. Typically what I do is after draining the fluid I put a couple of quarts in and fire it up. Get it to operating temp,run it thru all the gears and check, add, repeat until my fluid level is just below the full mark. Always go thru the gears, BUT do not move the vehicle. After adding fluid go thru the gears to make sure. Then test drive and check again. Then I check it a couple of more times within the first week in case of a small leak.
Recently I had a U-joint go bad on my 92 3.0L 2WD which damaged the seal on the trans. extension. As a result I had to replace both the U-joint and the seal and refill the trans. I filled it until I could see it just below the full mark. After driving for a short trip (less than 5 miles) the transmission began acting up. Low fluid, added almost another two quarts following the procedure indicated by 68torino above and have had no problems since.
But to answer your question, according to my Chilton's manual the 91 with 4.0L auto. trans. takes 9.7 quarts of fluid for the 4X2, add .3 pint for 4X4. But I have found that this is really a "ball park" figure. It is really necessary to follow the procedure detailed in 68torino's post. Fill slowly and check fluid level often to avoid overfilling.