Step one would be to run simcraft for your character. If you can't hit somewhat close to that number on a tank and spank fight, then there's something going on.
So I just hit 90 on my Warlock (my 9th 90, on my mission to pick a main for 5.2 as I'm sick of my current) and I'm drawn to affliction.
However, I can't figure out if I'm terrible at it, or if it's some low gear level scaling issues. My gear is at 464, and I'm barely pulling 40k dps in LFR. On my other classes at this gear level, I can usually pull at least 50k without much issue.
I feel like I'm not playing it terribly, picked up AffDots, refreshing DoTs when I get procs and will get full duration from Pandemic, saving haunt for procs, only using otherwise when I would cap shards.
Does Affliction just not scale well at low gear levels, or am I probably doing something really wrong that I haven't pinpointed yet?