HELP!!!

I own a 92 Pontiac Grand Prix, with about 150,000 miles on it. It used to run really smoothe with no sounds, smoke, lots of power and acceleration. One day the car just would not start. I had it towed to the garage and they said it was the Ignition Module. I told them to fix it and they did. I payed the $463.14 bill, went to start my car and it took me three trys to get it to start. I notice that the motor is skipping, and there was a cloud of blue smoke from the exhaust when i started it.The motor runs a okay but rough when going about 25-30 but when the car shifts into the lower gears at speeds like 40 - 50 the motor skips badly and it shakes the whole car, it's so bad! The mechanic said it needs a tune job. But the car ran perfectly fine before I brought it there, execpt for the ignition problem. So i guess my question is what could they have done to my poor little car? They have been jerks about the car as far as awnsering some of my questions. I really don't know what is wrong with it, or what to do. Any help would be so greatly appreciated. Thanks!