It's not the transmission most likely. It is the RPM load sensor that went tits up. You're going to have to unplug it. Finding it is not that hard as it is one of three plugs located next to the passenger side fuse box. Offhand, I cannot remember which one it is but it should only a 2 wire connector.

If this doesn't help, I have a known good transmission control unit you can test. If that doesn't work, it's probably in need of a rebuild since there are some stuck solenoids in the valve body and probably some shot clutches as well.

Try the RPM sensor unplug first, it won't hurt anything.