It will help to know which model you have.
Look for a stamped serial number on the vertical section of the RH side of the frame.
Appox 2-6 inches down and sightly in front of the door. You should find the S/N. It should start with a number like maybe 355 or 685. If it is a later model it may start with a different number. It will also help to determine if the transmission if acting any differently according to the direction. Normally, problems that are related to one direction only are more likey to be internal. Perhaps a worn clutch pack, or, internal leak from broken sealing rings, etc. Problems that effect both directions are likely to be either an inching problem, charge pump problem, or, converter.
Hope this helps a little.