All forward gears require the forward clutch to work. Reverse does not. It requires the direct clutch and low/reverse band. Either you have multiple part failures (bad clutch seals, burnt clutch disks, etc) or something is wrong with the pump or fluid feeding. Take the pan off and see if something is clogging the filter. If it's clear you might as well put a fork in it, because it's time for a rebuild.
You didn't recently have the filter off did you? There is a pressure relief valve/spring held by the filter. If that fell out you could have pressure problems.