For some reason i'm doing a little bit lower DPS as Lightning compared to when I do Full Madness. Something seems to be wrong
You are correct, something is wrong. It was the nerf from gawd during 1.2. I was Lightning spec Sorcerer until a month ago when I changed over to hybrid (20/21 - Lightning/Madness). It is a crying shame that one has to do this to put up any DPS numbers that account for anything, especially in PvP. PvE it is still passible but you still have issues of casting times to get off Thundering Blast, or trying to use Lightning Strike while hoping Chain Lightning procs up so you can fire that off instantly. The damage ability for Lightning is the worst spec for Sorcerer doing DPS. Right now, I run hybrid in both PvE & PvP; no need to change up until such time BW fixes the problem with the Lightning tree.