If I don't slam the shifter hard into high, there is a loud grinding noise when i mash the throttle before it slips into high. It goes into gear, but reluctantly so. I've changed transmission fluid and front/rear diff. Any ideas? Thanks

 

Try lowering the idle,plus if belt is grabbing the rear clutch or if it creeps in gear, hard shifting can happen.Plus this model transmission was bad on water entering the small gear selector cover corroding the gears. This alone can cause sticky, hard shifting. Part #3 is the cover and gears behind here were full of grease from the factory.
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I know when I was having issues like that I took the cover off and put grease in there. If I remember correctly there was hardly any grease in there at all. It made a big difference after that.