97 Dakota, lose of power, backfire, lopes in gear(repeat post).

I have posted twice before on this truck, and have received some well thought out, knowledgeable responses, but none have fixed the problem.
I have changed: Sparkplugs, Rotor, Distrib Cap, Sparkplug wires,
Coil.
I have convinced myself that the IAC valve, MAP sensor, Colant Temp sensor, Air temp sensor PVC valve, Compression, are all okay(right or wrong). I am aslo sure the Cat Conv(new) and exhaust system is Okay.
Only new clue is this. I put another new set of plugs, properly gapped, in and ran the vehicle 100 miles, and examined the plugs. All looked great except Cyl#4. The plug had been firing but there was a small carbon buildup on oneside of the ceramic around the tip. No sign of oil, or fuel(when the engine was cold I ran it 30 seconds to see if I had a wet plug- -I did not). From a previous post I said that: When I unplugged the fuel injector on #4 it made little or no difference.
Here is what I haven't tried. Timing Chain, Cam Sensor(checked with meter) . Crank Sensor. Fuel injectors (I and the mechanic at Dodge Dealership checked fuel preasure).
Any suggestion what I should check Next?????????? Oh, it has 135K 6 cyl. 3.9L 2wd.
Thanks; Rogerx
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The 3.9 had problems with bushing for dist drive gear would be worth checking
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<snip>
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If you switched #4 injector with another cylinder's injector, does the unplugging of the fuel injector that makes "little or no difference" follow the injector or stay with the cylinder?
FMB
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I haven't had the fuel rail off, but I see where you are coming from, and I will try it in a few days(more pressing problems). And I am also going to look into what Sqdance said about the dist bushing.
Thanks guys- -Rogerx

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