Mechanic Q: Why won't the car shift?!?

My girlfriend drives an 02 sebring convertible and it has been nothing but trouble. about a year ago it stopped shifting out of first gear and her father had some guy swap out the old transmission with a new one. Well it worked for about 2 months and it has gone back to not shifting out of first gear. I have hooked up the computer and it is throwing shift solenoid A, B and C malfunctions as well as some others that I cannot remember but afterwards I feel like it could be the TCM module. Where is that located or am I way off? what do you think?