Something to consider:
When doing mods, be sure to take a baseline dyno run and a post-mod run ON THE SAME DYNO, and note your % gain there. Different brands and configurations of Dynos give out different numbers - some are more forgiving than others.

Additionally, I dont know if the SRT6 has a 'DYNO MODE' option, but it's cousin: the MB //AMG C32 does.