I have a '99 Grand Cherokee Laredo and kinda recently it has been having issues shifting when I first start driving. If I let it warm up for bout 15-20mins it doesn't seem to do it but if I don't give it that long it acts like the transmission is starting to slip. Once it shifts a few times, after giving me some lip, she runs like a champ again. It only does it when it is cold out too, when it is warm-ish out (bout 60) it doesn't seem to have the problem. My transmission fluid is also fine. My friend says her car does something similar when its cold out and says its just acting up to the cold.

Any ideas on what it could be? I do plan on taking it to a shop but I have to wait a couple weeks as I'm away for school. I am just looking for some possible solutions/diagnosis so that I will be better prepared for what my mechanic tells me.
As I already stated my transmission fluid is fine and only serious answers. Don't waste my time with your stupid remarks.