2003 Nissan Altima not accelerating/bad speedometer

I had same, was told car locks down to low gear after some faults so not to damage the car. Take car to a garage that diagnoses via fault code (usually a free service), the fault will have logged a code on cars computer. Nissan know what the code problems are and the net holds many answers too, you just need to know the code then you can get it fixed !