So seeing as im basically new to this forum AND trucks i had a few questions that i figured someone could explain better than google.

1. I have a 08 4.8 silverado. Who makes a supercharger for this? and why doesnt the 5.3 one fit if its the exact same setup as the 4.8?

2. Me and my buddy have the EXACT truck. Both 08 short bed regency after-style, with 275/55 20 wheels and tires. The only diff is he has a 5.3 and makes 15 mpg and i make 12 in the city. Thats with a K&N, shorty headers, and 93 octane tune from nelson. I also have a cutout and im testing that to see if it helps my mpg any. So what im asking is, why does he get better MPG than me?

3. Id like to get the acronyms cleared up so i dont sound like such a noob spelling this stuff out.
what does nnbs, sss, ect. stand for?

this forum has been a wealth of knowledge so far
i really appreciate it, thanks in advance