Peerless 930 stuck in 4th and 5th

I pulled the transaxle for my drag race mower today cus it's been stuck in 5th gear since the last time I ran it, anyways I pulled it and everything looked ok and I poped it outa 5th using a wrench and worked it back and forth till it didn't catch anymore, put it back together and back onto the drag race mower hooked up the linkage and again got stuck in 5th gear. Does anyone know why this is and how to fix it?

Check for burrs along the keyways on the shaft, along the inside of the gears, and on the condition of the shift washers. Chipping on the keys can cause jamming as well.