Not having owned the camera myself I may need correcting but I did have a look over the firmware updates after
GregK8 made mention of it and I think you found your solutions, and you may possibly need to get a faster SD, SDHC or SDXC card to achieve max fps.
as for you complaint about the lack of 24fps, I ask:
Did you not read the spec sheet before you bought it??
High noise
; According to DPreview it is "One of the best APS-C DSLRs in terms of high ISO image quality" So I think you either need to shoot raw and run noise reduction software over it, or start looking to cough up some significant amounts of $$ and get yourself a FF or medium format gear instead.
I am not sure what more you could expect without paying SIGNIFICANTLY more money!