Hello, I have a 2018 with 38000 miles. 2000 miles ago, my check engine light came on while I was on a trip. I noticed that not only did I have the check engine light, but my exhaust brake and my downhill speed control did not work ( I had my trailer with me). I dropped my trailer off and was headed home and to the dealer a day later. On my way home (maybe 400 miles passed since the check engine), my power was reduced. Boy was I glad I did not have the trailer on!! limped on home, then dropped off at dealer. The said it was some sort of valve that needed replacing and I should have paid more attention to what they said it was. They also said my emissions sensor seemed dirtier that it should have been. Anyway, off I went & happy it was still under warranty. Fast forward to 30ish days and 2000 miles later, exact same thing is happening - 1) check engine light. 2) no exhaust brake or downhill speed control 3) just waiting for the power to be reduced....I just know it is coming. Going home tomorrow and will drop off at dealer next day. Any idea on what is happening?