Shifting Problems!!!Please Any Help???

Hi, I recently bought a ' 96 Cherokee W/ 180 000km. Recently I have been experiencing problems shifting (5 spd, in-line, 4.0 ltr). It is very hard to shift in/out of gear, especially 1st & 2nd. it' worse on the down shifts, and when it's hot out or once engine temp gets warm/hot. Sometimes it won't even go into 2nd at all, or it takes an extreme amount of force. There is no grinding (except occasionally in reverse) so I don't think it's a clutch problem(but if tranny is coming out clutch will be changed reguardless). When I first brought it home I went thru it checking/changing fluids/filters, and the tranny fluid was low. I topped it up and it took about a litre. I'm thinking damage may have occured there as I do not know how long it ran low on fluid. I have never owned a jeep previous, but I LOVE this one, so if anyone has any input or suggestions PLEASE HELP. I think I will be pulling the tranny next week to have a look. But I'm not all that tranny familiar.
Thanks in advance. And I must say this is an awesome site, I wish I would have found it sooner.
TIMMY T