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Discussion Starter #1
I have a 2011 Silverado 4x4 extended cab with a 5.3 that has 180k on it. About a month ago I noticed a slight miss at low rpms under a light load. Like going 45-50 mph up a slight hill and just giving it a little throttle. I got the truck with 165k so I've only had it a little over a year and decided I should swap the plugs. The old plugs looked good, no clear indicators of misfires or plug problems. Everything had that nice sandy colored look to it. Replace the plugs and it seemed a little better for a day or so and then it was there again. No codes have EVER been thrown for this issue. So, I figured maybe it was a coil pack. Since I had no misfire codes I went ahead and ordered a full set (no, not AC Delco, but as you will see it didn't matter) and replaced them and it still didn't go away. At this point I noticed my mileage had dropped a good 1 mpg and my tach was jumping about 200 rpm at random intervals when in this light acceleration, light load situation. You can hear the engine change although the 200 rpm is really hard to feel. I've put a graph below that shows fuel pressure in red and rpm in green. You'll see the little spikes in the rpms. I figured I was in deep enough now to do the plug wires and eliminate ignition so I changed those with no difference. After some research it seemed like a Throttle Position Sensor so I changed that today along with cleaning out the throttle body and MAF. STILL NO IMPOROVEMENT.
I'm at a loss as to where to turn next. The truck had the cylinder shutdown thing deleted so it doesn't do that and I am not sure if a tune has been put in it or if it just had that feature deleted. If I get on it the truck has good power - chirped the tires going from 1st to 2nd. It idles smooth as silk. The miss seems to come between 1000-2000 rpm and generally when you are under a load going up a slight hill. I think that's all the details I can provide. Any advice would be appreciated.
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It isn't a miss, a mis-fire will generate a code.
 

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Discussion Starter #3
So that would suggest a fuel issue. I forgot to mention that I did run a full can of Lucas injector cleaner last tank and this tank I put in a can of Seafoam. I also did the old trick where you suck about a cup of Seafoam up into the intake through the brake booster and then shut off the engine and let it steam clean. Then start it up and blow out all the carbon.

So my next parts to toss at it would be injectors, I guess.
 

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Mis-fires caused by apart and fuel will throw a code, I'm saying you don't have mis-fires.
I don't know what your seeing, perhaps a timing issue; but no codes means no mis-fires.

Edit, perhaps a torque convertors issue.
 

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Discussion Starter #5
Mis-fires caused by apart and fuel will throw a code, I'm saying you don't have mis-fires.
I don't know what your seeing, perhaps a timing issue; but no codes means no mis-fires.

Edit, perhaps a torque convertors issue.
That makes sense but I'm still back at square one and have no idea how to figure out what is wrong. I literally don't know where to begin.
 

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2000 Silverado Z71 4x4 5.3L 460k+ miles w/ GM rebuilt motor and trans
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Drive it around in 3 (or whatever NOT OD is on your vehicle...) and see if it still happens. @RayVoy might be onto something with the torque converter.
 
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