I had the exact same truck.....the goo news is they have true dualls all the way to the muffler! That means dual cats too! So what i did after not finding any cat-backs that i liked or thought were too expensive, was to go to a local custom exhaust shop......they made me a custom duall exhaust with an x-pipe for $300 all the way out the back and two chrome tips. I personally went a bit too large with 3" tubes and it "popped" a little on hard accerleration. if i did it again i would go with the 2.5"
And no you wont need to reprogram the computer...as long as everything else is still stock, like the air filter and exhaust manifolds....all you will need to do is dissconnect the compuet for 10-15min and it will re-learn everything about the truck and your driving habbits.....it may actually feel a little peppier when you clear the computer out too!