'00 transmission Probs

i have a '00 s-10 that has a weird tranny problem. After driving for about an hour or so, when the tranny is good and warmed up, its shifts out of 5th and into fourth and stick there...it can shift to 3,2,1 but not to 5th....someone please give me an idea as to whats wrong.... after about 10 minutes of stopped and cooling down it works fine...but then it happens again... HELP ME!!!!

Ok, I take it that it is a manual.

Check your manual transmission fluid level.

The 5th gear if the highest elevation level in the tranny and when the fluid dips, it is the first to lose its' lubrication.