I found myself in a similar situation. I've been MT'ing Kara for a while and am now spending a lot of time OT'ing because we have a paladin. It's not that he outgears me, its just he is useless when not tanking and I have DPS gear. If you are going to DPS in your current spec, work on your +hit until you are up to 140 then stack a bunch of str and your DPS should go from laughable to edging out a few of the lower end DPS. Doomplate can be a big help and you should be able to get quite a few drops your DPS classes already have while in Kara. For DPSing I go into zerker stance (unless I'm responsible for debuffing a boss or going to be taking a lot of damage) and use Devastate and Whirlwind. Duel Wielding will fix your rage starved problem and you'll find it difficult to not gain agro once your DPS gets higher.
I'm not sure what you mean by this. Hopefully you already have a mod such as Outfitter and can easily swap sets of gear. You will basically end up with 2 completely different sets of gear and swap between pulls.My avoidance/mitigation is, of course, going to only further hamper my rage development, so I'm having to down-gear as an OT, which leads to confusing decisions that aren't always the right path to take.