My 94 ram with 268,000 miles started pop and backfire. about a year ago plugs, cap, wires, rotor, coil, fuel pump, were replaced. Changed out crank sensor with a good used one, still does same thing. It will idle and rev in park but under load, any throttle past quarter or so and almost to wide open it backfires and pops and wont pull itself. At wide open throttle runs fine and til about quarter throttle. I am thinking throttle position sensor or pickup under distributor cap. Any other ideas before I start buying parts? Ever happen to anyone else?