Shutter and hesitation while driving

My 2002 ford f250 has 192,000 miles and has a little hesitation when accelerating, there is like an echo sound from both seperate pipes since I have true duals. But the driver side is making the echo worse than the other side. After it has finally shifted gears all I do is step on the gas a little bit but not enough for it to rev up while going around 50 MPH and the vehicle wants to shutter. Ive replaced the spark plugs and gapped them at.054 and when the engine light came on it said cylinder 8 was misfiring and I replaced that ignition coil but not the rest. The throttle position sensor has been replaced.I dont know what else to do. What else may be the problem?