[68GMCCustom]

Based on the trouble I had with a stand alone '09 designed harness on an '09 LY6 and for whatever reason used '07 Silverado VIN for programming...which found that the two's wiring diagrams are not the same.

As long as there are no harness issues I'd guess that modifying the '08 4.8 tune would be less desirable then starting with a '11 programmed ecm. They have to have a valid VIN I think too? as far as codes...I know a lot of that has been disabled on mine so that no weird error codes pop up.

I'm a firm believer of being able to see whats going on. Originally I used only my Aeroforce Interceptor scan gauge to monitor things, clear codes. Then I got HPTuners (comes with a scanner program as well as the editor) and WOW....there's a lot going on in there! I run scans...send to my tuner...and he sends me a new file to load via email. Couldn't be easier. I've "read" the tune on my TBSS also...but have not modified it yet.