My 2000 Caravan with 3.0 engine and 4 speed transmission seems to be stuck in second gear. It may be starting in first, but will not go any higher than 2nd. What could be wrong?

Its most likely in limp mode meaning that the transmission computer has found a problem. Take the van to one of your local auto parts stores and have them scan the computer. They usually scan for free. Write down all the trouble codes they get and post them back here. We can go from there.