2015 GMC Sierra Denali-catastrophic fuel pump failure

With it in the miles/time warranty it is either warranty parts failure or a fuel issue. If GM is refusing the warranty repair based upon water in fuel/contaminated fuel then check with your insurance company to see if this is covered under the comprehensive portion of your coverage. If so then the insurance company will cover the repair (less your deductible) and their subrogation department will attempt to collect from the fuel provider.