transmission problem?

last tuesday i was driivng down the highway when my car started to slow down and made a low pitch rumbling sound, when i opened the hood, i saw a little smoke, the coolant tank was bubbling, and i saw coolant pouring on the ground. i towed it to my house and looked at it and in the coolant tank it was darrk colored coolant. i disconnected it from the radiator and drained it out. at the bottom was a bunch of sediment so i shop vaced it out. when i looked in the radiators fluid was bright and clean looking before all the draining i did. i also changed out the therrmastat and the belt cuase it looked rough. i checked the oil and it looked like it was just oil and was full enough and i checked the transmission fluid and it was fine too, i thought it would be good to go so i drove about 8 miles to my dads. when i was driving back, it made the noise againso i backed off then it stopped and i made the rest of the way (which wasnt long) to my house, the temp was only at like halfway. when i got to the driveway, i went to repark so i backed up and iwhen i wasw going it just stopped moving. i opened the door and there was a very large puddle of transmission fluid (red) all over the ground. i looked underneath where the transmission pan is and it looks like it leaked from there. my dad thought my radiator was clogged but its not so he thinks its the torque converter now. does anyone know whats wrongg or has had this problem before? thanks alot

Welcome to AF, the car must be gotten on a lift, underneath cleaned up and the source of the leak determined, more than likely unless a coolant line let go the trans would have to come out.. BTW, in the future post the year, engine and mileage.

thank you very much. its a 1996 cutlass cierra with a v6 and 140000 miles. i guess i just better sell it then if the tranny has to be taken out... i bought this car for 450 thinking its was a god send but turns out it came from hell haha