i currently have a 2000 sierra 4.8l and i just bought a 2004 5.3l with a cracked head for 50 $, i'm pretty sure the 04's had most out of the box power, would switching the intake manifold and throttle body be possible or am i just wasting my time?

 

No gains to be had by doing so, the intake and throttle body have the same dimensions and flow numbers.

 

Nows yours chance start a build on the 5.3 build it and drop it in start with a set of good heads unless your gunna go S/C or T/C. But nows the chance to build and learn get TBSS intake if funds or tight or go fast lsxrt then cam and mail order tune