Now, I'll start by saying that I'm sure everyone on here has their opinions are certain products, brands etc, so I'm not trying to turn this into a this is bad, this is good, typical conversation when it comes to oil, additives, etc. I just simply wanted to document what I did and the results. To start, my engine was a chatterbox. It had noises coming from every part of it, loud noises. On cold start the noise was so loud that you could hear it from at least 20 or 30 feet away. This is my first Chevy in many years and I know everyone likes to say that these engines are just noisy, especially with miles, but I refused to believe there wasn't some way to quiet it down, so this is what I did.. Poured in some Gunk engine flush, idled for 10 minutes Changed oil, 5qt 5w-30 and 1qt auto trans fluid Drove back and forth to work for a few days Changed oil again, another 5qt 5w-30, 1qt auto trans fluid, 1 small bottle Marvel Mystery Oil Drove a few days again Changed oil, 6qt 5w-30 and 1 can Seafoam Drove a few days again 1 can Seafoam through the brake booster hose Hard driving up and down the highway, then drove a day or two 1 can Seafoam through the throttle body More hard driving up and down the highway, then drove a day or two Last oil change, 6qts 5w-30 Engine now runs as smooth and quiet as any other vehicle I've ever owned. Again, this is all just for documentation's sake. If you decide to do something like this, it's on you, I'm not responsible for whatever may happen, good or bad. Honestly my truck has 220k on it and I know it'll be needing a new engine sometime in the future, so I was willing to take a gamble on killing the motor by dumping a bunch of fluids into the oil, but it worked and now it's not embarrassingly loud anymore. Even on cold start, the thing sounds like what you'd expect a brand new truck to sound like.