Could it be the fuel sock?

My 2600 idles perfectly. When i take off it drives fine for a very short time and then starts to run rough. Next time I pull up at the lights and go to take off it miss fires. The longer I drive it keeps getting gradually worse. If I stop the engine it will run clean again for a very short time and then go back to running rough. If I turn the key off while im moving and then start it again while rolling it clears again for a short time.

I have replaced, plugs (Bosch which I read arent the best for these engines) leads and new fuel filter (injected). Also cleaned some carbon off in the distributor cap but haven't replaced it.

Could it be that its clogging up in the tank at the sock or is there another filter inline that I should replace?

Any clues from the description I provided?

Yes, it very well could be!
When my fuel sock clogged up, I could turn the key off for a few seconds, and then back on to get a few more miles before it did it again.
Bosch plugs are alright, as long as they aren't platinum.

Also... the 2600i has known capacitor issues in the computer.
Have you looked in there yet?

What year pickup is it? Also does the pickup smoke when this is happening?

Its a injected 94 model (i'm from Australia) and I havent really noticed any excessive smoking when this has happened.

The easiest way to check if the sock is the problem is check the fuel pressure while this is happening. It would be low and then come back up at the stop light.

Have to see how we go next Saturday. Ive booked the hoist at a friends house and we are going to drop the tank and have a look at the fuel pickup and sock and see how much crap is in the tank.

It's FAR easier to lift the bed!

What ^^^^^he^^^^^ said!

You can just tilt it also to gain enough room to get the sender out, just make sure it is well supported. But if you want to look into the gas tank, then remove the bed, I say!

Thanks for the great advice.. never thought of lifting the tray.

The only reason I asked about the smoking is that I have had (on a couple of different trucks) the crank angle sensor (located inside the distributor) fail. When this has happend to me, all three times it was causing the ecm to inject way toooo much fuel and when accelerating it would smoke black from too much fuel being injected. Just figured I would give that tidbit. Also like the other guys said check the ecm if the sock is not plugged. I am replaced the capacitors on mine before and it is not too bad of a process. I have only had good luck replacing them if you catch them before the leak their electrolyte all over the circut board. There was a durration of a couple years where the electrolyte was slightly acidic and was eating the capacitors apart and them gets on the circut board and causes that to fail. Good luck.