2003 Chrysler Voyager transmission gets stuck in 2nd gear. Symptoms prior to this include speedometer needle flutter and check engine light on.
It sounds like you are going into limp mode due to a bad output speed sensor. Scan the computer for codes. You will most likely get a trouble code for the output speed sensor and some gear ratio codes. Post back with the scan results and we will go from there.
Oh yea, most local auto parts stores will scan the computer for free. Write down any code/s and their descriptions and post them here.