http://gmauthority.com/blog/gm/gm-engines/l83/
Fun fact: the L83 makes more HP and torque on E85 (about 25 hp and 30 lb-ft).
It's making 300 lb-ft at maybe 1600rpm. That's pretty good for a 5.3L.
Previous gen 5.3L:
The old one also made more power and torque on E85 but not as much as the new one.
The new one should drive better. The old one holds 300lb-ft until about 3000rpm when it begins to head toward the torque peak. The L83 breaks 300lb-ft right at 1600rpm and just builds. Actually, it still builds after 3000 but it was already at 350 lb-ft (greater or equal to the old one's torque PEAK!) when it builds. The shape is pretty similar, there's just more everywhere, and it falls off less at the top end.
Now power delivery in vehicle depends on a lot of additional factors, such as engine management (torque management and fuel economy calibrations being the top two), and torque converter characteristics.
I recall Mike O'Donnell showing me in his old 2000 Chevy truck (3/4 ton) with the Vortec 6000 and 4L80-E. It had pretty sluggish power delivery but it was all masked by engine/trans calibration. With that stuff turned off, it drove like a different truck (and like you'd expect). The good news is, everyone that LS swaps ends up turning that stuff off so they get to experience the organic engine capabilities. Which is why no one who's LS swapped has complained about that stuff.