1989 Chevy Camaro car wont stay running

My son has an '89 camaro rs 2.8L V6 we just bought for his first car. It has ran really rough like its missing since we got it. We did a tune up plugs wires cap and rotor still not good. It gets horrible gas mileage like 5 or 6 miles to the gallon, now you have to push the gas pedal to the floor to keep it from dying and it will only go about 5 miles per hour if that floored and spits and sputters the whole time if you let off the gas it dies instantly? HELP we have a few Ideas but me being a single mom and no one to help us we dont know where to start looking. Some ideas were fuel pressure regulator, and someone said spun rod bearing which I dont believe it could be?
Thank you so very much for your time and happy holidays!