Case 970 shifting problem

[Jpip56]

Hello. I got a case 970 on our farm and it gets stuck in 3rd gear. The clutch in gauges and disengages but when you push on the shift it won't come out of 3rd. All other gears work great. I put a new shifting fork in it and didn't help the problem. If I take the inspection plate off the top of the tranny and use a screw driver to put it back in neutral it goes so easy. Looking for some direction if possible. Thank you.