NHTSA Complaint #11558217 — 2021 GMC SIERRA 1500

My 2021 GMC 1/2 Serria SLT 4x4 Crew Cab short bed, V-8 Gas engine with Automatic Transmission. I bought this pickup used with apprx. 41k miles on it. I had it about 2 months when I went out to start it and the battery was completely discharged, it would not even click or any lights come on. I hooked it up to a battery charger and got it started, took it to a shop and had the battery and alternator check which both were ok. Drove back home and went out the next morning and the battery was completely drained again, got it started and went an put in a new battery. 16 days later it did the same thing this time it smelled like wires burning when I opened the hood. Called the dealer I bought it from and they put it on a diagnostic machine for over 3 hours could not find anything. Then next morning the battery was again completely drained. Got it started and took it to another shop to get it checked out and after almost 3 hours there they found nothing. Came back home an it sat for just over 40 hours and again the battery was completely drained. I could smell what I think is plastic or rubber when I opened the hood again. My main concern is that this may be a fire hazard and could not only burn up my pick up but my house as well. The check engine light has came on but goes off so I am at a complete loss on this and seems as if GM is not concerned either. I have tried contacting GM but so far nothing other than a note from GM Canada that I need to contact the GM USA, and again that is the only thing I have gotten from anyone. Perhaps this is just a odd thing, I don't know but I do know it is not a safe thing.