2013 Chevy Silverado 1500 cruising vibration

[Hgasperson1984]

Does anyone else experience really bad vibration while cruising around a 45 mph while the truck is in V4 mode? I never noticed it until my truck hit 105K miles and I now have 136k and it has gotten worse. 

[CamGTP]

If it's only in V4 mode to me that says it's something with that system and the transmission. 45mph should have already put it into 6th gear and the engine is kinda lugging at that low rpm. Add in the fact that it's dropped 4 cylinders could make it worse. It's like the engine is fighting to stay in 4 cylinder mode and not wanting to unlock the torque converter. I'm sure if you let off the throttle the vibration goes away but comes right back once the converter locks and it drops into V4 again.

[Hgasperson1984]

Correct it's only when it drops from 8 to 4 cylinders in D. If I put it in manual and only set it to 5th gear I don't have the issues