Blown Transmission or Just Need To Replace?

Ok you can start laughing i have a 1993 chevy corvette (automatic) with ready...288,000miles. while i was driving i went down hill and i push on the gas and it just goes up to 5rpm. i pull to the side and tried to switch gears (D),(D1),(D2), and reverse but non of it clicked into gear no movement what so ever even when i push on the gas. Its at the house now i look at the transmission fluid its black so im not sure if the tranny blew or if i can still replace the fluid