I have a 2020 Silverado 1500 Custom 4.3 V6 with 42,000 miles. The oil pressure gauge keeps going to zero and alarm goes off then it says to shut off engine. I took it in to have it look at GM Dealership they did a diagnostic check and found nothing. They checked the oil presure and said it was good. They can't get it to do it so they say they can't fix it because they don't know the problem. Last night I drove my truck again for a hr and it did it probably six time while driving 70mph on the highway. Any suggestions what to look at and change so it works properly? I can't continue to drive it like this?