Have always used synthetic and regularly change my oil. 50,600 on truck now. Truck runs like garbage. Bad hesitation/jerking/missing under throttle going up even slight hills. Feels like a transmission shudder. MDS sounds god awful with audible detonation/spark knock. Dealer confirmed rapid misfiring on a previous trip and replaced a “broken” MDS solenoid they claimed was broken when they pulled it out. Regardless it made no difference in the truck at all. Still knocks. Truck hasn’t thrown a CEL for misfiring.It's unlikely that a bad lifter would have made it this long. You need to try a third dealership or an independent mechanic. Odds are this is manifold related. How many miles on the truck now?