Misfireing on all 8 cylinders with no codes, or service engine light?? on 2004 GMC Sierra 2500 HD

A couple of weeks ago my 2004 GMC 2500hd started misfireing while driving. I took it to a GMC service center & they don't know whats going on with it. They have never seen this type of issue. It produces no service engine light nor codes. They reset the computer & after about 30 seconds it starts all over again, misfireing in order. they checked all of the sensors, fuel pump etc. no problems noted. Any ideas??

Asked by for the 2004 GMC Sierra 2500 HD
I have a 2006 2500HD and it is doing the same thing, did you ever find out what causes this? Had it to two different shops, no codes, replaced everything but still have this sporadic issue.
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I don't have a answer I have the same problem. My fuel pressure is about 45 to 48 psi. A mechanic said it should be around 60 psi. all the time. I don't know anything else. I hope I/we can fiqure this out.