2" will be plenty of pipe for your engine. Stay away from the hollow mufflers like Flowmaster. I like the DynoMax brand, they flow good and have a deep rumble to them. A straight through muffler will be pretty load and rap a lot. Use 2" tail pipe and you will be happy.
If you like the sound of noisy 6 cylinder, go with 1 3/4" pipe with the muffler right up under the cab and the longest tail pipe you can get, your neighbors will love you!

Joe