dan smith explained to me that when it rolls back it changes the pressure on the front of the gears to the back and can make it stick,,,,,,,,,,,"solution" use the brakes when comming to a stop, i know this sounds stupid,, too simple but it works, especially if i give it just enough brake pressure to make the tractor slightly rock like he explained, it works perfectly, keeps the back pressure off the gear and shifts smoothly. i rarely use brakes before, now i will. so a slight change in operator habits........problem solved........