Vibration

[JojoGMCHELP]

Hello everyone,  I bought a Denali 1500 brand spanking new in 2015. Since then I've had issue after issue and even ended up with a brand new engine with 25k miles. 

Since the engine was replaced or maybe once before i have noticed a vibration that seems to be when I accelerate and feel like i am driving on rumble strips. It has been happening on and off for a month now. (No worse no better than the day before)

This issue has been fixed by the dealership at the least 3 times and hell maybe 4. I have looked through all the service paperwork and cant find the information on what was fixed. I have contacted the dealership and they are saying that they have absolutely no information on what was fixed/replaced/  i want to say that they told me once that something was reset!!