2003 Ford Taurus car will not go into gear

I have never had any problems with my car. Until today. I started it up, put it in reverse, and the car felt like it was still in neutrual. No warning no nothing, just drove car last night and then today, its like its stuck in neutrual, checked the fluid, my brother said it looks like its about 2 quarts over filled, I have never, ever added fluid the 3 years i've had it. So he is saying there is a blockage somewhere. I want to have it towed this week to aamco, but i'm so worried they will tell me I need a new trans just to make money. How do I know if I should trust.