HELP! I dont know how fast im goin...

First thing to do is figure if the cable is broken.

One way is pull it off the trans, and drive it with a drill, have a friend watch.

Or pull the speedo end loose, and see if you can turn it. IF so, the cable is obviously not connected to the trans.

IF the cable seems OK, pull the plug out of the side of the trans, and inspect the gear, if it looks OK, insert the cable and make sure the square drive does not slip.

Check the "plug" that it is installed correctly. There's another post illustrating this, here:

http://www.forabodiesonly.com/mopar/showthread.php?t=137442

Still another way is to pull the cable off the speedo, get the end where you can see it, and after safely jacking up the rear and blocking the wheels, run the car in gear to see if the cable turns