before retiring (again) my company went thru $875,000-$950,000 in bearings every year, nachi,nsk,ntn and koyo are some of the best bearings on the planet. the ones to avoid are china and some of the eastern block brands...
on the clustr shaft, 3rd gear is held in place by a snap ring, it is very common for the ring to break allowing the gear to move around. if you pull the pto cover on the side of the trans you should be able to tell if it moved or see witness marks. the fix was a simple piece of tube in between...
pull the pto cover and see if 3rd gear on the cluster is moviing around. it is only held in place with a snap ring unless updated.. very common problem....