Looking for possible assistance with the vibration issue in my wife's Tahoe. It has this vibration at very distinct speeds., 25-29, 45-49, 59, and more. It is very noticeable when accelerating smoothly, non aggressively. The vibration is so prevalent that it is felt in the seat and throughout the steering wheel. It has been to the shop twice, the last time I took the mechanic with me and he witnessed the vibration at the low speed, we didn't get on the highway at higher speeds. I left it with him for a day, he states its the DFM switching back and forth with cylinder deactivation. Seems odd to me that it does it a those exact speeds and its constant when at those speeds. I cannot recall this truck doing this when I picked it up upon purchase nor a few weeks after owning it. My next test is to set the cruise while its vibrating on a smooth road and see if it changes if the truck accelerates going up hill, if its the DFM, it should deactivate due to load and all cylinders should fire and vibration should stop. If it doesn't stop, I believe it would be something else. Your thoughts? I do like the truck, but the amount of money this truck cost, I should not be dealing with vibration issues. Thanks in advance.