take to a tuner and have him tune the transmission and do a before and after data scan. GM's new transmission hardware is great, it's the software that is the problem, its great for sipping fuel and good mpg, but long term durability is lacking you'll be lucky to make 100,000 miles stock tune , a reliable trans tune will cure the problems your having to experience with vibes and a lugging motor. dont forget to do the trans re-learn after the tune or a flush..
many owners before you lost thier minds chasing vibrations, by replacing everything that spins on these trucks, only to find out it still shook and vibed...lol