I was driving today, and when the car downshifted, it made a clunk noise. After coming to a stop, and trying to drive the car, the car wouldn't really go anywhere. I was close to home and drove it home. When going down slightly inclined streets,slowly, the transmission shifted o.k, but when trying to accelerate, or going up a hill, Its like it completely disengages. When I got home, I put my foot on the brake, and gave a little gas, it slipped and made a few clunk noises. What do we have????