Lock ups during full speed download

Hi all,

I'm currently running a WNR3500Lv2 as my main router with Shibby v110-AiO Tomato Firmware. It's connected to the internet via a Cisco modem; my internet connection offers me 100Mbit/s download and 5Mbit/s upload speed. There is no problem with throughput - I can easily reach 120MByte/s on a local network (transfer between my NAS and my Workstation); also, I don't have any problems, if the servers on the internet allow it, to reach full speed (which is about 105Mbit/s).

However, my router gets unresponsive whenever I download at full speed (everything above 7MByte/s). The download doesn't get interrupted, but I can't browse any websites or make any new connections, as long as the download is running. As soon as it is finished, everything works fine again. The router webinterface is also unreachable during that time.

QoS is disabled, so is bandwith logging and other RAM-consuming stuff. I got about 110MB of free RAM, and about 8000 free NVRAM left on the router. When I look up the webinterface after the download has finished, it says, that CPU loadtime is at about 5% for the last 1 min. There doesn't seem to be a CPU limitation; I guess, there is some kind of a loop or something like that. Does someone have a 100Mbit/s+ setup, which runs fine at full speed, without any problems? Or does someone even experience the same problems?