One problem related to manifold/header/muffler/tail pipe has been reported for the 2021 GMC Sierra 1500. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2021 GMC Sierra 1500 based on all problems reported for the 2021 Sierra 1500.
Engine burning oil and blowing white smoke out tail pipes. Have to add oil every 1500 miles or sooner if towing. Has been an issue since first oil change. Vehicle is now at 88057 miles.