Running problems

I have a 95 chevy corsica with 175,000 miles on it. At first we were not having any running problems at all. Now, once we hit 50 miles an hour, the car acts like it is stalling and will not go any faster. I checked the spark plugs and wires and the plugs are working properely. I checked the coil pack on the number 3 and 6 cylinder. When I pull the plug wire off the coil pack, nothing happens with these 2. When I check the other one's, the car almost dies. I changed the coil pack and still have the same problem. Can you give me any ideas? Someone told me it sounded like a failing injector. Could this be a possibility? If so where are the injectors located?