Asus RT-N10U Black slow wired speed when in ap mode

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Hello i have a problem with my Asus RTN10u router , i have purchased this device in order to use it as a AP in collaboration with my RT-AC66U Router.
The wired setup follows
modem---RTAC66U(router mode)-----RTN10U(AP mode)----pc (Win 7 64 bit/elementary OS)

Here is my problem , everything seems to work fine the n10u takes my wired connection and creates wifi AP and also acts like a switch for my pc

The thing is that copying files between two lan pcs (wired both) is really slow (1MByte per sec instead of 10 or 12 for 100Mbps connection)

When my pc is directly connected to my router with a wired connection i can copy files between wired lan pcs with no drops in speed but when the rtn10u sits in the middle i have 1/10 of the speed.

modem---RTAC66U(router mode)---pc (copying speeds up to 12 MBps)
modem---RTAC66U(router mode)-----RTN10U(AP mode)----pc (Win 7 64 bit/elementary OS)(copying speeds up to 1,2 MBps)
modem---RTAC66U(router mode)-----RTN10U(AP mode)---wireless---pc (Win 7 64 bit/elementary OS)(copying speeds up to 1,2 MBps also)


I have tried several things , my network card is not the issue because it works fine without the rtn10u , the OS is not the problem tested with several other OS same issue.
I have tried several flavors of OS for the router including ddwrt , tomato , same issue (although tomato seemed to identify the lan speed locked on 10Mbps instead of 100Mbps but i could not find a way to fix this)

Could somebody please help me ?

Thanks in advance ,,
yannis