Misfire at start up

[Graphite Silverado 2018]

Got a 2018 silverado lt with the 5.3l v8. It has 13000km on it. Since new it has been misfiring when starting up in the morning for about 5 mins. Until i get it going and then it runs fine. Pretty much if you leave parked for about 6 hours it will misfire. Took it to 4 different gm stealerships to find out what wrong. Nothing was found but misfire still there. No engine lights or anything on dash. Engine sounds a little rough too. Any ideas on what it can be? 

[mojohn]

I got it too.  2017 Silverado LT 30,000 miles

[lapoolboy]

On 7/26/2019 at 12:50 AM, Graphite Silverado 2018 said:

Any ideas on what it can be? 

Yeah, it's the GM LT1.  

[Graphite Silverado 2018]

GM LT1, but whats the issue wit it? 

[Graphite Silverado 2018]

Its not lt1. It has the ls3 ecotec engine. All the dealerships say just drive as is. When it fails it will be covered. 

[lapoolboy]

33 minutes ago, Graphite Silverado 2018 said:

Its not lt1. It has the ls3 ecotec engine. All the dealerships say just drive as is. When it fails it will be covered. 

It is not the LS3.  It is an LT-based engine EcoTec3.....RPO L83.  

 

[lapoolboy]

How do you know it is misfiring?  Do you have a scan device connected that is reporting misfires?

[Graphite Silverado 2018]

Its not throwing any codes or anything. But on start up for about ten mins of driving after, it stutters a bit and sputters at red lights. Then after 10 mins runs like new

[lapoolboy]

What RPM is it idling at after warm-up?

[Graphite Silverado 2018]

At warm up its at about 900-1000. That after intial start up.

[Graphite Silverado 2018]

And yes my mistake not ls3. Ecotec3

[lapoolboy]

What RPM is it idling at after warm-up?

 

Does it settle down to around 550 RPM?

[Graphite Silverado 2018]

Not really. It stays at around 800-1000. Just cant seem to figure out the misfire. Ill take a pic of it warmed up and where the rpm sits. 

[Graphite Silverado 2018]

Do.you think it can be factory plug wires or plugs? 

[Graphite Silverado 2018]

Yup warmed up stays at 700rpm