[Dunwich]

To test your spell rotation go see Dr. Boom in Netherstorm. Stand over in the rocks where the bomblets can't get to you and fire away at him.
As for Gruul's; First question, were you in charge of the enslave on the wild fel hunter. If the answer is yes then cease to worry about DPS. Just like in Mag's where you will be responsible for the banish/fear of infernals you should not judge performance based strictly on DPS. If the raid is successful and no one dies (especially if no healers die) because you did your job then you're the lock to have around. Want to see lousy DPS, go tank Leo...but then dare anyone to say you weren't vital to the mission. Look at the big picture. Many guilds fail to get past Gruul's/Mag because of the focus on DPS and they forget the little jobs that have to be done and done well.
If you were there just for DPS...well, go see Dr. Boom.