Tahoe LT, 4.3 Vortec, w vin.
If I VERY SLOWLY give it gas I can get it to redline. If I accelerate normally it coughs and sputters real bad after about ¼ throttle. I have replaced the EGR valve, Throttle Pos Sensor, O2 sensor, Cap and rotor and fuel filter. I am not getting any codes and neither is my mechanic with much better test equipment. He also said all other systems that he was able to monitor were fine. When the problem started it took about 30 to 45 minutes to appear, now it does it within a few minutes of starting. I did find a short that my mech is going to fix. The pos cable was shorting against the motor mount bolt a few inches in front of the starter. I am open to any and all suggestions. I NEED this vehicle to run right.

 

It may sound unrelated but check you cat. converter...if it's starting to break up inside it'll act as a check valve and if a piece rattles around and gets stuck in the outlet side the back pressure will prevent you from getting much above idle. I had the same thing...replaced pretty well all ignition parts, ran perfect at idle but wouldn't go over 1500 rpm. If you can, pull the O2 sensor and see if it's any better, this will give the exhaust somewhere to go if it's plugged off.

 

There are 2 wires (1 red 1 blue) going into the plenum low on the drivers side in the front. I pushed about an inch of slack into the plenum and my engine died. I relaxed them back a bit and now my engine runs fine. Though it’s not truly “fixed” yet, at least I can go to work tomorrow and when it does crap out, I know where to look.

I have found this problem or very similar ones described in several posts but only a couple have posted a resolution. It was only after way too much searching that I found someone mentioning that he found some worn wires going into the plenum