Welsome to LS1truck.com! DamnYankee is one of our Moderators here and is a good guy. He also has a really nice truck that has a monster motor--that we swapped not that long ago... You picked up a good vehicle--not need for worries about reliability on that thing--as long as you don't get too crazy with the mods! The weak point is the tranny, so keep the mods to a minimum and you'll be fine. Sorry to hear about your 5.9...
To start off with, I would recommend doing a CAI and some exhaust work (if the wifey doesn't mind a little rumble. You could do some mid-length headers to improve the lower and mid-range torque numbers. A new muffler is needed too. You could also do some 05 stock e-fans and some pulleys. Besides that, a custom tune needs to be done as well. Contact
Allen Nelson for all of your tuning needs.