well being a nerd I downloaded verified stock tune files for each 2000,2004, and 2006 Chevy Silverado 5.3L V8 trucks. The tunes are very different. I'll post some screen shots in a sec. BTW, the 06 file is from my truck. The biggest gain from the tuning was the PE. Stock the enrichment rate is really slow. I wouldn't enter PE until late 2nd gear. Now off the line it enters PE and is so much faster.
jake

 

Well I couldn't really get a good screen shot of each, but here's the differences in .txt files. Looking at the tunes definitely shows how the trucks are differently powered each year.
Jake