could be your valve body is gunked up or possibly your OD shift solenoid. You could drop the pan and give it a quick clean, it's pretty simple and straight forward. just use a big table and keep track of all the small parts and what order they go in. I washed my valve body in gasoline and a bunch of 'silt' came out and it looks like new.
at the same time look at the filter and check the magnet see how much metal debris you are collecting. Also the snap ring on the a518 are know to break apart. that might be causing the shift issue as well. you'll probably find parts of the ring in your pan as well. You'll need a new pan gasket, I think they were still using cork in 92.