Wont go over 20 mph

The car starts right up (has check engine light on) and the transmission will go through the gears (when front an back of vehicle is jacked up). I do not think the transmission is bad, but when you take off it will go through first and into second gear, but instead of accelerating, it is like it goes back into a neutral state. The speedometer still goes up but the engine just revs. And when put in park it makes a noise like the park pin is not catching right an the vehicle will still roll in park. The transmission fluid looks and smells good. Could this be a transfer case problem or linkage or even a sensor?