Griz,
Lots of guys like those Flowmaster systems. Most models are too noisy for me. With the modern trucks, I have had good experience with a single 3" system from a company called Gibson. The performance will be noticeable, and it will not sound like some punk-ass kid's IROC. Borla makes a very nice fitting system, and comes in stainless steel. The price is pretty high, however.
You do not want your exhaust straight out the back if you tow. It will blow crap all over whatever you have behind you. If you don't tow, then go ahead.
If you are having a local shop do the work, ask them if you can hang around to see and listen to some of the types of exhaust work they do. You may be surprised at what you like and don't like.
Dynomax makes some excellent mufflers for trucks. I put one of their high flow round industrial models on my father's big block motorhome. It really pulls the hills better, and you can definitely tell that it has a 460 in it. It is not noisy enough to upset even that grumpy old man either!
Good Luck