I realize this is an old post but I wanted to add my comments now 6/2015. I started having this problem (Shuttle shift popping out of gear when loading the transmission, I.E. Taking off in second gear, scooping a load of dirt out of a pile while in gear, etc.) I am sure there will continue to be those who will search for an explanation of what is happening to their tractor just like I did. I was grateful to find the information I needed right here and felt inclined to add the additional part information and a cost estimate from the dealer.
I purchased A used DK45S with 389Hrs on it, I now have 790 hrs on it and had the shuttle shift fork repair job done at Ellisville Tractor in MS, they did a great job, it feels better than when I got it. They removed the steering column to gain access to the cover where the fork is located. They replaced the fork, (was worn probably 1/32nd on each side as describe in other posts) shifting arm, fork rod and several other small pieces. While in the area, they also adjusted the clutch. If you let that go too long without adjusting it, you will be splitting the tractor for a new one. I like to fix my own stuff to save money but this job was too technical for my skill set so I decided to get it done right the first time and spend $512.58 to have it done. BTW, your back will appreciate having someone else do it. Here is the parts list, see below. They charged 4 Hrs at $85/Labor Hr ($340) and $117.70 for parts and the remainder was bobo charges (Tax, shop supplies, environmental fee, etc) I asked the mechanic about the job, he confirmed the replacement fork is a little beefier than the original and the reason he put in the other parts is, "It didn't cost that much to have the assurance the other parts were not also bent or worn", I agreed.
T4620-22163 Fork Rod $25.95
04811-00090 O-Ring $1.00
T4620-22153 Shuttle Shift Fork $56.95
07715-01605 Ball $1.00
62331-18532 Spring Stopper $2.95
T4624-22121 Shift Arm $21.95
0481100160 O-Ring $1.95
T4624-22221 Packing V $5.95
