There are several places that will do a custom tune on your PCM if you send it to them and they are much better than an add on programmer. Wayne Hartwig used to be on this list, but is still around, did one for me that really woke one of my 5.3s up. Let them know your intake and exhaust mods so they can factor that into the tune.
So I have been thinking the same thing as you, my 2500 pulls awesome but I want a little more power in the bottom end. I was talking to a buddy and he said something about running a lq9 tune on a lq4 and it's supposed to help gain a little more power. I've been thinking about getting a Dyno tune for mine, also heard good things about that. Some people are claiming 50hp gains but that seems a little too good to be true, I know these motors come fairly detuned from factory. Also, I have a flowmaster catback on mine, dual in single out, and it isn't obnoxious but it's got good sound to it. Anyways, good looking truck!