Alright guys and gals. I have done enough reading and searching that I have no hair left. I have a 2000 silverado 4.8 ECSB 5 speed and she has about 221K on the clicker. About 4 months ago i started getting a weird miss around 50 mph when i was trying to accelerate in 5th gear. I didnt pay any mind to it as i thought it was due to the cats being orginal and over 200K miles on them. I installed long tubes with no cats along with new O2 sensors as well with a tune from wait4me performace to make every thing happy. Still had the stumble after the header install so I just chalked it off to the computer relearning everything. Fast forward to now and the slight miss is now extreme chugging, hesitation, and popping through the intake. Normal cruising is fine unless I put it under load. For example trying to accelerate from 50mph in 5th gear or trying to accelerate from 35ish in 4th gear. It just just stumbles and hesitates. If I try accelerate hard in first or second it will backfire through the intake and exhaust. It will still pull rpms and mph but it feels restricted. Almost like a carbed vehicle trying to drive off when its to cold. I have cleaned the throttle body, installed a new TPS, replaced the MAF with a known working clean one, new fuel filter, clean dry flow AEM filter with a K&N intake tube. The fuel pump was replaced about a year or so ago. I am not throwing any codes either. I am going to reset the computer by disconnecting the battery and turning the key to the on position to drain any power in the system. See maybe if some of the values in the computer are jumbled and need to be flushed. It did seem to run better for a day or so after i replaced the TPS sensor since i had the battery disconnected for the time i installed the new sensor and cleaned the throttle body. Anything thing to check look at would help as I am at my witts end with this thing.

 

broken valve spring or really really really worn out heads...

 

I'm hoping there is a new timing set in that mix somewhere? Really sounds like the chain and sprockets are worn out. If not, then it's most likely what BlackGMC said above.

 

Yeah still all original internals. I bought the truck with 111K on the clock and have have put almost that on it in 5 years.

 

Id say the valve train, worn camshaft lobes, worn lifters....my 5.3 was worn the fruck out at 173k

 

Have you actually checked you fuel pressure?? Sounds like what mine was doing when the line from the pump to the top of the bucket busted, it was getting fuel just not enough when under load. Just a thought...

 

The fuel pressure and the FPG are the next two things I am going to look at tomorrow when i get home from work along with resetting the computer. I am leaning towards a fuel issue since the truck has no drivetrain noise and regular driveability is fine. Just when the demand for more fuel is needed it seems to haave these symptoms. Now the other strange thing is that when the truck is in neutral it will clear rev to 6k with no issue at all. Only has the problems when engaged in gear and under load.

 

W4m tune get rid of, then do what others above have said

 

Your not loading the engine when free revving it like you are in 5th gear at 50mph and half throttle. Its not demanding near as much fuel.

Check your fuel pressure while driving, how bout new plugs and wires while your at it?

 

Do a compression check? Thats where I always start...