Auto gear changes not smooth and rather slow

My w202 sometimes takes ages to change up when i am driving. This seems to happen around 3 and 4th gears and the engine will rev and get loud before changing. It also seems that if as i do more miles the changes become smoother and more normal. i notice this when i drive the car first thing in the morning

What could possibly cause this. one time the revs went up dangerously then it finally changed

Dont want to end up with a hude repair bill


Cheers