I have a 1964 john deere power shift that will not come out of gear in park. I can put the tractor in park and let go of the inching pedal and the tractor will move forward. the tractor will move in all gears forward and reverse when in reverse the engine will lug down and want to die. I had to split the tractor because the rear main seal was leaking so i pulled the first clutch pack out and all of the clutch disks were free c1, c2, and PTO. I had john deere tear it apart to make sure nothing was wrong internally but it was fine. Every time i sift to 3rd forward gear the tractor stops then goes. So i took the control valve off and cleaned the four shifting valve they moved freely up and down and did not have any free play in the bore. The shifting linkages have no play either. The park pawl must not be working the only way to stop the tractor is to use the inching pedal and brake or shut it off. Not sure what else to check any suggestions. thanks