Router capping speeds?

My router, a D-Link WBR-2310 REV A Firmware 1.04 seems to be capping my speeds for an unknown reason.

My network was

Modem >>> Router >>> PC
>>> Switch >>> Xbox 360

I was getting horrendous speeds, with speed tests on my ISP (Eastlink) showing my download 49% Worse.

So I change the network around

Modem >>> Switch >>> PC
>>> Router
>>> Xbox 360

And now I seem to be getting speeds 25% BETTER than other Eastlink customers.

Only problem is, I like the router's security, so is there anyway to remedy the problem?

Thanks