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Q: Truck is running real rough and loading up like too much fuel on 1994 Nissan Pickup (D21)

I changed the fuel filter and it seemed to be better but now it is a lot worse, barely runs. When I'm on the freeway and i give it gas it wants to die like it's getting too much fuel and loading up, especially at higher RPM's makes a backfiring sound (not too loud though) It lacks power and gets terrible gas mileage. I'm thinking fuel pump but not sure need to fix it this weekend so i can make it to work on monday....
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If it's getting so much fuel enough to make it run that bad, you should be seeing black exhaust smoke. If you were to check the plugs, they'd be black and sooty. You need to check the ignition system for good spark, you need to check the sparkplug wires and distributor cap & rotor. You need to check the air filter. It's possible the the airflow meter is failing, that could cause real bad running. Those things come to mind first.
You may need to see a Nissan specialist, and make plans to get a ride to work.
Here's a directory link for you:
Thanks for your response, I actually did the plugs, cap rotor, air filter and inspected the wires real good last weekend hoping that would help to no avail. They weren't really bad at all but the cap was pretty worn, no soot or smoking. I dropped it of at friends shop yesterday and he did a quick evaluation and said he thinks its either somethin to do with and injection or more likely a backed up cat or exhaust issue. What do you think?
Did he find anything with those issues. I have a 90 nissan D21 and it is doing the same thing.
Actually, Superbob was right on track, after loads of trial and error (because the diagnostic machine was drawing a blank) my friend noticed that the coil was making a strange interior clicking noise and decided to check it. Changed the coil and igniter and bam runs like a top. If theres no smoke or soot, I'd bet on a spark issue!
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