Just been out, smooth as butter back into 5th2-3 it could just be you beating the synchros, could be wear to the synchro or dog teeth on the gear itself.
4-5 my money would be on low oil and the plastic wearing down or worn off the selector fork. drive along in 5th, pop it in to neutral for a sec, let the clutch up, dip clutch and pop it back in to 5th and see what it does.