em0 and tunnel performance problem

[OxY]

hi!

i have an intel etherexpress gigabit card on 100mbit port and fbsd 6.0-p1..
my box is a proxy, it's traffic is 100/100mbit constant..
unfortunately i have to use tunnel and that is the source of my problem.
when i enable the tunnel and the packages are going through it the 
performance is poor..
it seems that it's not full duplex, the speed is around 50/50mbit, and have 
10-15% packet loss..
i tried to enable/disable polling, and used these sysctl vars:

kern.polling.enable=1
kern.ipc.somaxconn=2048
net.inet.tcp.inflight.enable=0
net.inet.ip.portrange.randomized=0
net.inet.tcp.sendspace=65536
kern.ipc.maxsockbuf=786432
net.inet.tcp.delayed_ack=0
net.inet.tcp.newreno=0
net.inet.ip.intr_queue_maxlen=1024
net.inet.tcp.blackhole=2
net.inet.udp.blackhole=1
net.inet.ip.rtmaxcache=1024

without tunnel the speed is 100/100mbit, great.

ps: with linux its all OK, but i wanna use fbsd :)