sounds like it is low on fluid, or wrong fluid in trans. If someone used the wrong fluid(even the all tranny stuff) one bottle to top off will make the tranny act silly. To properly check your fluid level(just had a tranny problem myself and a lot of trial went into figuring this out) warm the vehicle up to temp, apply ebrake, put foot on brake, shift trans thru each gear then leave it in neutral. Check fluid level should be in the hot zone on dip stick.
Overfilling these transmissions makes them act funky as well. When I bought my 2006 LJ it would shift like crap and seemed to slip. The PO topped it off with the wrong fluid and over filled mine.
I filled mine up short when I changed the filter, to make sure I did not overfill and when going thru the gear while it was low it was acting like how you described.