Acceleration hesitation with lack of low end power...2011 5.3L Silverado

rc_rosealetta · August 27, 2018

2011 Chevy Silverado 1500, 5.3L Vortec Engine, Z71 4x4. Approximately 123,000 miles. Purchased new 12/2011.

The backstory: Approximately 2 years ago, I noticed a bizarre "wop wop wop" sound that emanated from underneath the middle of the cab (between front passenger and driver). Noticed it happening at low speed (25-35 mph) and 2nd to 3rd gears. The speed/frequency of the "wop wop wop" correlated to the speed i was going, ie faster I was going, the faster the wop wop was. It was more apparent with towing my horse trailer(approximately 6000#) and going uphill than not towing and on flat land. Once truck got into 4th gear, the sound disappeared. Took the truck 3 separate times by the local dealership and it was never able to be replicated and they could not find anything wrong. I then took the truck to a well known GM transmission guy that opened his own shop and had him look at it. He couldn't find anything wrong with the transmission itself and stated he has rarely seen transmission issues with that model year/transmission. That noise stopped on it's own after about 4 months and has never returned. Performance was NEVER affected and hauled fine. Just did the weird noise for awhile.

Fast forward to the past 4-5 months. Noticed truck having some acceleration problems when going from a deceleration (around a corner, slowing down to prepare for a stop) to acceleration again without coming to a complete stop. When I would get back on it, it seemed to not have the power that it used to, and seemed to take awhile getting back "into" it. This is MUCH worse with hauling the trailer I mentioned above. Also worse with going uphill. Sometimes it feels like the truck might not make it up a smaller incline. There was a "dead spot" on my accelerator it seemed, so I replaced the Accelerator pedal position sensor as well as the throttle position sensor. That improved the problem minimally. Not sure if this is related to the random issue I had two years ago or not. It starts FINE, it idles FINE, otherwise it seems to act FINE. Truck has not been abused whatsoever. What I haul (occasionally) is well within the capabilities.

NO CHECK ENGINE LIGHTS EVER/NO CODES.

What I've done so far:

Replaced/flushed transmission fluid- 6/2016 (before current issue)

Replaced transfer case fluid- 6/2016 (before current issue)

Routine maintenance has ALWAYS been on time (oil filter, oi, air filter, tire rotation, etc.)

Clean/Flush fuel system- 6/2018 (no effect)

Replace all spark plugs- 6/2018 (no effect)

Replace TPS- 8/2018 (helped minimally)

Replace APPS- 8/2018 (helped minimally)

Sea Foam through gas tank x2 - 8/2018 (no effect)

I'm finally giving up and taking into the shop on Friday, but I'm not holding my breath that they can recreate it or that they can figure it out.

HELP?!?!?