Car wouldn't Move!

I have a dodge neon 2002 with 82,000 miles. It has a 2.0 liter engine. It had been making a strange noise maintaining speed between 40 and 50 mph. This noise happened on the highway which then caused the car to jerk and then maintain speed but with higher rpms. Once I left the highway and came to a stop. The car when pushing on the accellerator would just rev the engine with grinding noise behind the left wheel well. I turned the car off and then on again. It would move forward now as long as I kept it under 10 mph. Once I would go over 10 mph it would slip out of gear and only rev the engine when I pushed on the gas. I called some mechanics and one suggested a trans specialist who I took it to. After looking over the car he said I needed the transmission rebuilt. Prior to this incident, I had an air filter replaced during an oil change. They left the air intake tube unattached, that I did not discover until a week later after my car jerked and back fired going up a hill. Did I really need my transmission rebuilt or could it have been another problem? And could the overlooked reattachment of the air intake tube to the air filter have caused any of this?