'15 GMC 6.0L 3500 Random Misfire 8700 Miles - Help

BearOleMiss · February 8, 2019

Hello everyone. I operate a business and have several work trucks, most being 1-ton's with flat beds, with welding machines on the back. The last work truck I purchased was a brand new 2015 GMC 3500 with no bed. I installed the flat bed and put all my welding equipment on it here at my shop. The truck worked flawlessly for the first year or so.

I run a welding fabrication company and my rig trucks are pulled into shop and locked up each and everyday. Some days the trucks will be cranked up for 1-2 minutes and pulled out into the front of shop. In the afternoons they will be pulled back in and locked up. This could happen for several days in a row or maybe a week. Sometimes they will be run everyday on local jobs and run 20 miles or less. I take care of all of my equipment and do regular oil changes when necessary.

The particular vehicle in topic is a 2015 GMC 3500 HD with 6.0L gas burner (8'700 miles). It has passed 3 year warranty. It has had selected "bad" spark plugs replaced maybe 12 spark plugs in total. The truck would start running bad while driving and start to have a hiccup and bad idle/misfire. I would take it to the dealership and they would diagnose it with a random misfire in cylinder "x" and they changed the plug in question. The cylinder(s) were mostly different each trip in. I would receive the truck back, codes cleared, and the truck would continue to run like a top for several months before issues arose again. I would take it back and they would change the spark plug(s) and problems gone. I don't have the code on hand at the moment but I remember hooking it up to a snap on diagnostic tool and the code was random misfire. I vaguely remember the code being p0300. I have since bought OEM spark plugs myself once. I hooked up diagnostic tool and it showed cylinder #7 had a misfire. I replaced #7, cleared code and issues went away for months. The problem just came back again this week and I am near sick of changing spark plugs on a vehicle with 8700 miles on it. What should I do, what could be causing this issue?

Let me know if any more details would help.

Thanks, Bear.