don barling

Hi, I got a transmission problem on my 2000 Harley Davidson edition. The truck has been driving fine no slipping or noises or anything to suggest my tranny was on the way out. Oil and filter change 5000miles ago and oil still looks clean and smells good on dipstick.. However jumped in it the other day (parked downhill not using emergency brake) selected Reverse and it would not move more than a inch , rev counter and engine note dipped as if engaging gear .I moved my other car out the way and put the truck in Drive and it moved fine the 20 yards down the road till I needed to turn around and use reverse in doing so, It would not budge not even in Neutral, so had to lift rear off ground with trolley jack and get my family to push me backwards to make the turn. Then drove it forwards back to where I started now facing up the hill and went indoors to drown my sorrows! Next day I got in it again and now it wont move forwards or backwards its completely stuck as if its engaging gear as the revs drop but not disengaging park is that possible?. I disconnected the prop to rule the axle out and it moves fine. Any thoughts/advice or experience of this would be much appreciated. Thanks.