I also have a 3500A backhoe. It has no movement forward or reverse most of the time. Sometimes after sitting for a long time it works fine, both directions and does not slip. It is a hydrostatitic drive with the 2 flat pedals on the left side of the floor. Charge pump pressure is good, servo pressure is ok, pump servo moves when pedal is depressed. Pump servo can be seen by taking a small plate off at front of trans. With 10000 psi gage on high pressure line, gage shows nothing. With 600 psi gage, it shows charge pump pressure, about 210 psi. When observing the pump servo through plate, there seemed to be a lot of oil splashing around and the trans was filling to the point that I had to shut it off, or it was going to overflow. The thing that gets me is that it works 100% when it works and as long as you leave it running, it will work all day long. Shut it off, and you tow it home. Anyone with any info on this or perhaps a manual with hydro diagnostics would very much be appreciated. Thanks.