1992 Ford Thunderbird Transmission Issues

Ok, so I have a 92 thunderbird, I bought it about a year ago from people who didn't take care of it at all, they completely ran it into the ground. So now I am having problems with it. So the transmission has been a little iffy since I got it, but if I baby it and don't drive too far, or for too long it works perfectly fine. The other day, I was on my way home and the car just totally stalled out on me, no matter what I tried the car would not move forward at all. Even in Drive, if I took my foot off the pedal it would just roll backwards. Reverse was working fine so I was able to back up in and get myself into a parking lot and out of the middle of the street. When I opened up the hood, the coolant and oil were low, so I filled both up and had my friend come help me push the car home. I let it sit overnight, and when I checked again in the morning the coolant that I just put in was gone! When I tried to drive it to see how it was doing, as soon as I even barely touched the gas pedal the RPM gauge would immediately spike to 5 or 6, the speedometer wouldnt go up and I couldnt get the car to shift, so I was stuck at around 20 miles/hour. My friend looked and said that he thinks the radiator is cracked. So my real question is, what can I do to get the car running again, if I replace the radiator will it help enough for me to be able to drive the car again or is there a combination of things that I need to fix. Thank You! (Also, my mileage is unknown, the gauge is broken, so I put the number that it is stuck at)