2018 Silverado engine stumble when cold

[SM370]

I have a 2018 Silverado crew cab with 5.3L engine and 6 speed transmission with 25000 miles.  The truck has what seems like a misfire and rough stumble while driving 25-40 mph while the engine is cold, not up to 210F.  The issue is present when in 4 cylinder or 8 cylinder mode.   I keep it in L (keeping in L5 to stay in 8 cylinder mode) until the engine comes to normal operating temperature and then the problem goes away.  I took it to the dealer and they could not find anything wrong or duplicate the problem.  There are no error codes identified or problems noted.  The problem is more prevalent in cold weather, but is still there at Louisiana summertime temps.   Anyone else seen this?

Thanks,

Gary

[Doublebase]

Yes, very common I'd say. It feels like sort of a "fish biting" sensation...when a fish is biting your bait and you feel the rod. That's the way it felt for me, others have said the same on this forum. I think the direct injection perhaps has a little low speed pre ignition going on when the engine isn't warned up, and it goes away when it is.  

[Chad2919]

I have a 2017, which I purchased new with 5miles on the clock and now has 29k. Does this very SAME thing! Even when up to temp and in 6th/OD slight load or slight incline down the highway, I feel a random "fish bite" but absolutely no codes and dealer has not been able to find issue after many visits to dealer. Any resolution yet???

[steelerdude15]

There is another post on here about this issue. The post has a tsb in it. I believe the tsb says to change the fluid and filter. My truck would fishbite for a couple of minutes when the truck was cold. Since I changed my fluid in the pan and filter at 30,000, it doesn’t fishbite as bad. I’m thinking it still does it a little bit because it still has old fluid in it since I didn’t flush the transmission.

[Steve Barnett]

I have a 2017 gmc with the 5.3 . has done the same thing since new . took to the dealer , they said , no light no problem. My truck only has 20k miles and runs like crap until it gets warmed up.

[Chad2919]

It's my engine that is stumbling and cutting out before it's up to operating temp, I can even watch the tach bobble a bit when it does it-for the most part it runs like a carburated engine with stumbling and sputtering with rpm fluctuations that get sharper and more abrupt when driving 25-34mph @ 1000-1400 rpms until it reaches about 170 coolant temp. Then when it's up to temp it has the occasional "fish bite" sensation at low rpms at steady highway speed-55 or 80 doesn't matter. It's even more perceptable while pulling a trailer but it happens so abruptly when hot that I cannot perceive the tach bobble when feeling the "fish bite". Mine has the 6 speed and unsure how this is trans fluid/filter related but you have me considering that I may be experiencing two separate/unrelated issues... All of which, the ECU is not finding a misfire...but it feels like a misfire.  I was convinced that it is an electrical/sensor situation whether it be the Throttle body servo/mass air flow sensor/or the drive by wire peddle sensor or maybe even a coolant temp sensor or crank position sensor...but the dealer refuses to evaluate without codes in the PC.  I appreciate you suggesting possibilities and options to research!