Transmission not shifting

Our transmission is having difficulty shifting into gears. It will give a hard shift when going into first gear. Second and third go in a bit more smoothly, but fourth never goes. In every case, the shifts are very late, and the rpm's are very high before it will finally shift.
I tried changing the VSS but that only made it worse. When it gets to around fifty mph the speed needle tends to flutter a little, not excessively, but enough to notice it. When I tried the new VSS the needle went crazy.

We are not sure if it is a different sensor or if we just need to take the transmission for a overhaul. It was fine, we made a long six hour trip with it home and then out of the blue this started. Your help is greatly appreciated. Thanks.