Hadn't seen this issue resolved in these forums so wanted to share my experience. 2018 Chevy Express 3500 bought at 100k miles. Around 110k started showing signs of shaking when accelerating at low RPMs while towing a load (5x8 uhaul trailer). Never showed a code so the OBD reader couldn't diagnose anything.

Thought it was the transmission so took it into the dealer around 120k to get a full diagnosis / flush. They said everything was good trans wise and the fluids looked clean.

Van started experiencing a stumbling feeling when accelerating around 1500rpms, this time without towing a load. Still no codes so wasn't sure what it was.

Towed a 5x8 trailer again around 123k and this time it started getting worse, stumbling really badly around 1500rpms especially up hills. Tow mode would help but even then it had trouble when in the lower rpm zone. Finally, the check engine light flashed at a slow rate until it stayed on, spitting the P0300 code.

Well, took it to the dealer again to diagnose and they say all of the spark plugs and connectors are shot. Most likely due to some long drives in high heat.

Currently waiting in the service lobby to get it back and will update if anything bad happens after this. But the fact that this never spit codes until it got this bad is baffling to me. Regardless, if this has happened to you, check your spark plugs!
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~ Alan Jackson Fan

 

Van is running like a dream, towing a heavy 5x8 trailer with ease up the Blue Ridge Mountains today. Might have to take a special trip down to the Chattahoochee.

 

Do you think they were the factory plugs? I'm ham fisted but I've always broken at least 1 plug wire when doing plugs so I always replace them when I do plugs.

 

thanks for keeping us up to date with the solution