There is such a thing as a throttle body upgrade.
However, if you have not already done several other power releasing mods - longtube headers and catback exhaust, heads and cam and valvetrain, better intake manifold (you already have a pretty good one), larger fuel injectors - you'll find that a larger mouth and/or nostrils alone is not in and of itself going to release that much power, because it needs bigger better lungs and stronger legs first.
If the throttle body is NOT the engine's chokepoint, upgrading it won't release any power.
Also, if you don't yet need to upgrade the injectors AND the intake manifold, you don't NEED a better throttle body.If you haven't had your vehicle tuned yet, you should.
Besides tuning, the best bang for your buck in terms of dramatic effect would be
4.10 if you have a 4L60E
3.73 if you have a 6L80E
And yes, both require tuning.
This idle relearn procedure only applies to throttle-by-signal, yeah?
Every time I cold start my '02 Tahoe L59, the idle briefly exceeds 2000RpM before settling for about 1000RpM, and it takes about 3-4min before the idle gets down to 600RpM.