My transmission gets harder to shift as the engine warms up. It has 108,000 miles on it. I changed the oil but id didnt change.

 

What year/car/tranny? Do you have a short shifter? How's your motor mounts?
What oil did you put in it?

What do you mean by 'harder to shift'? Harder to get in/out of gears (gets stuck/won't go in), can't find the gear, etc?