Forget mufflers and TB's. The former is for sound change only, and the latter is worth no extra hp.
Your best bang for the buck is a tune and CAI. That combo is good for approx. 25 rwhp, and also gets rid of the notorious "throttle nanny". Good deals and great tunes are available from numerous suppliers, such as BamaChips, Brenspeed, and others. Suggest going with a 93 octane tune to maximize hp.
Another good performance upgrade is gears, specifically 4.10's. There's no hp gain, but the additional mechanical advantage increases acceleration.
And if you want to invest in getting the last ounce of performance w/o installing F/I, then there are long tube headers, offroad X and H pipes, underdrive pullies, electric water pump, drag radials,
suspension tweaks, etc.