RX 580 "lite"?

Hi, a few months ago i bought from a reputable spanish seller called Pccomponentes a RX 580 Sapphire Nitro + lite 8gb. I have not found anything about this "lite" version anywhere on the internet. It is clocked to 1340Mhz which i think its weird and the voltage is 1175-1200 mV. I am having less frames than expected in a lot of games and i am wondering if there is something wrong with this card. Do you know anything about this "lite" version? It has a 2 year warrant with the store, do you think i should ask them to give me a new card?