MTP have a lot of rejected shares (duplicate) in all pools less zergpool, but in zergpool less hashrate
Which version are you using?
5.6.1.3.b5ip3
Did you try another pool. Mintpond seems working well
Tried

Work fine 20-50 shares and after a round of duplicate shares, then valid shares and then duplicates, only work good zergpool but with low hash
I suggest add "-w 64".
If it still not working, try "-d 0" to see if one card works or not.