NHTSA Complaint #11438132 — 2016 GMC SIERRA 1500

-Engine gas consumption states 21 MPG Highway, 17 MPG combined and 15 MPG City. -When I started using vehicle during the first weeks and months the best MPG I could geta at the highway was 18.5 MPG with top-tier gas. -Ever since I bought the vehicle, the gas MPG have gone down around 0.5 MPG. The vehicle feels that it has to use more gas in order to perform the level of task everyday. -The motor oil pump at times moves down from the 40 mark to the 20 mark when idle at traffic light and it starts moving, it temporarily goes to the 60 mark. At other times when idle it stays in the 30 mark. -The transmission is an 8 speed automatic. It has issues shifting 1st and 2nd gear, and at times 3rd gear as well. When driving at slow speeds like in a traffic jam, mall parking, do a u turn or when you slow down at the traffic light and then turns green and you start accelerating again it feels harsh on gearing up and down. -This vehicle has the Active Fuel Management (AFM) system, it turns on even at slower speeds and you feel how the engine and transmission struggle to accelerate, go a gear up and push the vehicle with only 4 cylinders. Like in manual transmissions when you accelerate on a higher gear than the correct one, it takes forever to accelerate and properly change to 8 cylinder and establish the correct gear and ratio. -Even if all 8 cylinders on it it feels like if I am running on a smaller engine. -There was a fix done to the transmission for a valve, but the vehicle still runs the same as before. -There is a knocking noise starting to build in the engine. Best mileage I can get driving the same and gas is 13 MPG combined. -The recent safety recall for the breaks is actually making the breaking worse than before. -My vehicle is 2016 GMC Sierra All Terrain V8 5.3L 4WD Z82 with 36,500 miles on it and is doing all this and its getting worse little at a time.