I really want to start adding some mods to my truck but can only do it one thing at a time ( 8 month old girl ). I need some suggestions on what to start with, Intake, exhaust , guages, tuner? I am wanting to add about 120hp. Any suggestions?

Call JODY at DPtuner, he'll set you up with what you need and tell you what else to add and make it work.
http://www.dp-tuner.com/

You could start by trading it in for a Duramax.

start with an exhaust system, a 4 inch exhaust would be perfect, 5 inch if you plan on major mods, after that your gonna want an intake, and finally a chip, after all these mods you'll be looking at about 150 horse, depending on the chip