'04 performance upgrades

Looking for some advice on upgrading my wife's Tahoe to have more power for towing. I really don't want to spend too much so I'm looking for some help on what inexpensive mods will yield results. It has the 5.3 and has about 50k miles on it. Thinking of starting off by getting a tune up done but I'm not sure if a standard tune up is going to do anything that I can't do myself like new plugs, wire, air filter. Is their anything else included on a standard tune up on these things? Mods I was considering were upgraded air filter or CAI system, wires, plugs, possibly exhaust(don't really want to spend on a cat-back system and don't want drone). Would a muffler yield any results? How about a chip or tuner? Throttle body spacer? Any advice is appreciated. I'm not new to the performance market but I'm not sure what works best on these engines.