Often high engine RPM and sluggish or no transmission function can indicate poor modulation valve operation. So, first thing to try is remove
modulation valve plug on transmission valve body. Extract valve spool and observe if the small plastic filter/orifice is loose. This orfice/ filter has an O ring attached, remove O ring and tighten the plastic orifice.
A very common problem with early Daewoos and Doosans and if caught early a transmission failure can be avoided.