It's an updated big block based on BBC architecture, not LS architecture.
Cylinder heads are not bad but the exhaust manifold studs are small (M8x1.25) and break often. I was always replacing them on a 3/4 2005 Suburban i had years back.
TBH, i wasn't real impressed with the power that truck made.
What basic things could you do to make more power and maybe gain mpg