While driving 40-60 mph (speed where problem is the greatest) any time the truck is accelerated but not to the point it downshifts the truck constantly shakes/shudders. As soon as I back off the gas, the problem disappears, accelerating again repeats the problem. It's best to describe the problem occurs is when your "lugging" the engine. The shake/shudder happens numerous times a second and is not an even occurrence. It does take a smooth road to separate the truck bounce from the shudder. I did take it to the dealer, they ran their analyzer and took it for a ride, they claim they couldn't find an issue, or they couldn't repeat the issue. This is becoming more and more annoying now that i'm aware of what it takes to repeat the issue. Most of my driving falls right into the speed range where it's most apparent.