A833 getting stuck in 3rd gear

When you do a quality rebuild, you want a new or almost no wear countershaft, O/D main housings have slop built in at the countershaft. It should also have new bearings, bushings, thrust washers, and seals. Synchros need to be looked at closely. Check the interlock levers on the side cover and the 3-4 shift fork and 3-4 internal gearshift lever. Maybe even the side cover. Something is allowing the 3rd gear fork to over travel.