05 Pacifica won't shift from low to high gear

I have had this EXACT same issue before, it is the input sensor and/or the output sensor that needs replaced. The sensor, being dead, can't give feedback and decides to put your car in 'Limp Mode' (your car can't go above 1st or 2nd gear) which is basically the car's way of saying that it can't find enough info on the transmission and in order to preserve itself, gets stuck in 1st or 2nd gear. I had the 1st gear issue and coundn't exceed 22mph without the car sounding like it was going to kill itself. It is a generally non-expensive(NOTE: I did not say it is cheap!) repair and can be fixed without being TOO hard. Hope this helps.