i take it is a overdrive in a shadow??
or a van
if its stuck in 2 it is in limp thats what they do
it so you can drive to saftey
you can try changing the 2 speed sensor
1 that is between the 2 trans lines right above the selinoid pack
the other is straight across it about 8 "
the 1 will moe than likley have a bunch of 'crap' on it
there will be you're issue
these are mangnets on the ends so they only pick up metal
so you can guess whats wrong after that