Re: 2000 e 150 4.2 misfire cylinder 6 P 0306
Well, a couple possibilities that I can think of is a bad/about-to-die cat converter, or you have a faulty fuel injector (which you said you replaced; I'm guessing on all cylinders). In any case, once the fuel tank gets low, add a couple fuel injector cleaners and throw in five gallons of 89 octane with it. Run it until it gets low and then fill with whatever unleaded fuel you want.
Second, I'd get the fuel pump tested and if there is an inline fuel filter, be sure to have it replaced.
I'm also assuming the new spark plugs were gaped correctly.
'11 Ram Quad Cab 4x4 SXT 5.7L HEMI (stock); 48,500m
'06 Pontiac G6 GT 3.5L 220hp; 64,000m
'12 Chrysler 200 Limited 3.6L 283hp; 28,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!