You can get the GM Borla exhaust at ShopChevyParts.com for about $1,000. I installed mine in the driveway with the help of my son. I was able to drive the truck up on 8" blocks which allowed enough clearance to get the stock exhaust off in one piece. The Borla kit is really nice, fits perfectly, and was easy to install. Probably took 2.5 hours start to finish taking my time. I listened to a ton of sound clips online but don't think that is a very good way to judge the true sound because it sounds a lot meatier when the engine has a load on it. It will roar when you get on it, quiets right down when cruising down the freeway but you still know it's there. The best sound is in town stop light to stop light in Tow/Haul mode .
See ShopChevy at link below.
https://www.shopchevyparts.com/sierra-1500/performance-c-1456_4466_4467_4478.html