Cat 953 Doesnt move SOMETIMES

I have a 1998 Cat 953 (2ZN02121)that runs great most of the time, but sometimes on start up it will not move in either direction. I can shut it down & leave it & come back later or the next day & it may or may not move. When it moves, it runs great like it was a new machine.When it doesnt move, I dont know what to do other than leave it alone. Any ideas?

Cat 953 Doesnt move SOMETIMES