DIR 655 does not support jumbo frames.... The switch in it is also somewhat suspect as far as speed is concerned. Having a Gigabit switch is one thing. Lots of manufacturers just sped up their 100 speed switches to gigabit speed thinking no one will notice as 90% of people plug their pc into their router, connect a couple wireless clients and access the internet via adsl/cable/whatever. Because that internet link is usually slower than a 100Mbit link most people never notice the switches limitations.
Most people on this forum are different from the 90%. We have networks that do many things at the same time, streaming, internet access, storage access, backup and all that. Having a true gigabit switch (like the D-link DGS-1005/1008) where the buffers and underlying switch was designed as a gigabit switch uncorks your network and everything speeds up.
I learned all this as I fixed the freezing problems with my IPTV installation. Internet comes in via a 10Mbps router. 1 link from there to the wife's pc and 1 to the rest of the network. Everything past there connects to a DGS switch, even my dir655 which runs as an AP.
I can run two audio streams (Squeezebox's streaming FLAC), two video streams (IPTV and o!Play), surf the internet and access my nas at better than 19mbps.
Its the hardware guys - and not everything is what it says it is on the outside of the package.