Ok i'm about ready to pull my hair out so i figured i would get some advice from my fellow mustang owners. I will first off admit that i am a mustang noob so i don't know much about what too look for. I have a '91 GT that aside from a cold air intake and exaust, it is stock. A few days ago i added 1/2 qt of oil and some coolant, drove the car home and parked it overnight. The next day i go to start it and it feels like its missing horribly. I take the car to a shop they say that they ran a compression check on the engine and that i have two weak cylinders and that was the problem and the only way to fix it would be to rebuild the entire engine. Can two cylinders go bad overnight? i mean when i drove it home it was running great. I have recently replaced the plugs and plug wires. Is there anything else that i can check before biting the bullet and having a rebuild done? I apologize ahead of time for my noobiness lol....