I'm having transmission problems on my Toro walk behind. Last season the tranny started acting up on me. I pull a velke and use 4th and 5th gear most of the time. In a forward gear, it would pause and jerk repeatedly like clockwork. It was as if it were doing it whenever something might have rotated to a certain point.?. It was noticeable mainly in 4th and 5th gear. My dealer recommended changing the shift keys, I did. I could see definite wear on the keys. It ended the problem I was having. A couple months into this season it started doing it again. It was doing the same thing except this time I was also getting a chattering sound occasionally and when that took place the mower would not move forward. This was mainly on turns. It sounded like something was grinding or as if it were slightly getting out of gear but the shaft was still turning. I thought the keys might need replacing again but was unsure why they would be worn so quickly. I changed them and sure enough, the old ones had significant wear on them. It ran like it should up until a couple weeks ago. It's doing the same thing it did before I changed the keys last time. I pulled off the top of the tranny and the keys aren't worn. What else could my problem be? Might the inside of a 4th and 5th gear where the keys rest be worn since I use those most? I've searched around this forum but haven't pinpointed the problem I have.