Using just about any Auto Setting (AWB, Av, Tv, AutoISO, Fully Auto, etc...) is going to slow your maximum burst rate (but not usually by too much). Shooting in RAW will slow it down tremendously. Shooting in Manual Mode will give you the optimum burst rate (all other settings being the same). Shooting continuously for a few seconds will eventually slow it down. Cards can also be an issue, but you shouldn't be experiencing any issues with the card that you have - the maximum burst rate is typically tested with much slower cards.


Also shutter speed will obviously play a role if it's too slow, but by the time you get to shutters speeds that do, you're not likely interested in continuous shooting (e.g. 1/30s or slower).