Watchguard firewall 1000 throughput

[ew8]

I have seen this issue posted a few times, but I am confused about a solution. Plus bear in mind I am a developer, and not a hardware guy.
We recently installed 100Mb line, and inside the firewall I can get 12Mb-up and 7Mb-down. Outside I get the full bandwidth.

What should I check on the firewall that could be giving me such a drop?

Any help would be appreciated.
Thanks.

 

[RegTellis]

I am going through the very same thing with a different box, but I can tell you that the first thing you want to look at is that your nic configuration is identical on the firebox and also where you plug into the switch at on your LAN i.e. if your nic config for your trusted is set for auto or 100 mb full duplex, , then the port the trusted cable is going into on the other end needs to be the same. Also, you want to make sure that the external nic for the firebox is set to 10 mb half duplex.