My car won't rev any higher than about 1000rpm?

I have a carbureted 1980 ford mustang, with a straight 6, automatic , i was driving along today and then out of nowhere my car would'nt go above 100rpm's and consequently won't shift therefore I can't go faster than 10-15mph. I don't think it's the engine though because it's not making any odd noises what so ever, and it starts just fine. but it looks like the carbureted is moving about an inch to the side when i give it gas what is going on can anyone help?