Repost from the general troubleshooting board, they recommended I come over here...
2014 LT Z71 with 4.3.
When the cylinder deactivation kicks in and the truck switches into V4 mode, it has a very noticeable vibration or shake. Not unlike driving on a washboard road. This is not a wheel balance / driveline issue, it's definitely when the cylinders are deactivated and it's pretty much like a light switch. Anytime, any speed, the truck is in V4 it's shaking. Engine is totally smooth in V6 mode with all cylinders firing.
The shaking occurs the entire time the truck is running in V4 mode, NOT as it transitions in and out of it (as most of the other guys seem to have indicated). The entire time the truck is in V4 mode, it feels like it's driving on a washboard road at all speeds and under all driving conditions. V6 is perfect.
DIsclaimer: I "inherited" the truck from my dad, who swears it never had any vibration, but I felt it driving the truck home from his house for the first time. My dad also doesn't know how to put gas in his own car, and is the sort of person who goes into a dealership and says, "I would like one car, please."
Thanks,
Darel