It really depends on what your comparing it too. The LS family of engines is amazing, great power, and fuel economy. They also produce better torque curves than old school SBC's. If you are coming from a mild cammed 350, then a mild cammed 5.3 LS will be awesome. A little more difficult to compare it to a big block.
Just my experience. I originally had a mild cammed 427 in my 71 C10. It had a Th350 with 2000 stall. It was pretty quick for a heavier truck. I replaced the 427 with a bone stock 6.0L with a decent cam, and kept the same tranny...
The 6.0L smoked the BBC.