Download h2testw and test the SD cardI might add be careful there are many fakes out there. I bought a Sandisk Ultra 32 GB from Amazon which I suspect is a fake now... (only about 20-27 MB Reading and about 20 MB Writing)
Then Go to the SD association and download their formatting tool.
If the problem still persists, open up windows disk management and delete all partitions. Then create a new FAT32/exFAT partition for storage
If disk management did not work, Load up GPARTED on a Live CD and try to delete all partitions and create a new FAT32/exFAT partition like above.
If all fails, then you have a confirmed fake.
*EDIT* I thought you meant 27 MB storage, not read speed. Still, just run h2testw and confirm it.