M4N82 sli config and pci e slot config monitor readings

Hi and thanks to anyone willing to help me I`m still a newb. I have an asus m4n82 with dual nvidia graphics cards sli configured in pci 3 slots 1 and 3 as per manual instruction. I have physx enabled but when I check my nvida monitor it has pci 3 slots 1 and 2 at 5000 mhz and slot 3 and 37,500 mhz. I`m not sure if it`s only using one graphics card, or the I have it configured wrong. It just seems that all the output is coming from the one card and the other two slots aren`t detecting the second card. Thanks again.