Chevrolet General Motors Failed engine in 2015 Silverado pickup with 27000 miles. Chevrolet denied warranty coverage. Detroit, michicgan

We bought 2 new 2015 Chevrolet pickups for our business in May 2014.  One of the pickups developed an engine knock in July 2015 that turned out to be caused by a bad rod bearing.  Without removing a single bolt to try to determine the cause of the problem, Chevrolet denied warranty coverage because we changed oil ourselves and the pickup came with free oil changes for the first 24k miles.  We ended up paying an independent shop $8,500 to replace the engine and related components.  We will never buy another GM product, even though I have had at least 1 GM car for 49 years...usually 4.