Nebraska

I bought a 2020 AT4 WITH A 6.2 ENGINE. I bring the truck in to GMC for all oil changes. I was about 5120 miles. The car information stated I had 27 percent left of oil life. That night the warning light came on said I was low on oil. I was about 2 miles away from the GMC dealer so I drove up went in and the salesmen went grabbed me a quart of oil. The service was already closing so I went in the next morning. I had the oil changed and they said they would do a consumption test. 1000 miles go in and the oil level is ok. 2000 miles the oil level is ok. 3000 miles the oil level was ok but the oil look very dirty. 4000 miles I went in no oil on the dip stick again. I told them to change the oil at 4000 miles because its dirty and no good. They said they would call GMC and ask them what to do about the oil lose. 10 or so days go by no call so I go back to the service department. I just took a trip so I was already close to 1000 miles. They said they weren't going to do anything because they don't know what the problem is. They need more evidence bring it back after another 1000. I really pissed off today and was wondering if anyone has this problem. How they fixed it or what did the dealer tell you. Thanks for any help.