I have a 90 f350 5.8L and started out with losing spark so i replaced the plugs, wires, coil, ign. module, and then after replacing the distributor(and getting it top dead center on the #1) got it to run, but it runs with a real bad surge or hiccup..so then i adjusted timing to see if i could get it better(even checked to see if i'm 180 out), no luck. Took it to a mechanic to do a diagnostic and they said it showed a misfiring problem, but didn't provide me with codes. So I replaced the fuel filter also..replaced map sensor.....Could it be the T.P.S.??? And how do i replace it? Please Help!