Well your intake system is where you can start. (and it's where I started) "K&N" manufactures reasonably priced air intake system replacements and filters. The K&n air intake system replacement for your year tahoe runs about 290.00 and the filter runs about 60.00 give or take. It's relatively easy to install and is well worth it. You add about 20 extra horses (give or take) and torque.. just off of that! You will feel it too. Also the K&n air filters can be cleaned off and re used therefore lasting a LIFETIME! No more buying replacement air filters. This is where I started with my 99 Tahoe and I was and still am satisfied. Later, you could replace the exhaust system to high preformence.
Also I'm not sure when u had ur last tune up, and but replacing spark plugs and wires, and cleaning injectors can make a world of a difference. So the tune up is definitely important and a great place to start as well.
Hope I was helpful