slow internet 2701HG-B router modem?

I have a Siemens SpeedStream 4200 modem and a Dynex DX-E401 Router. Right now my internet is nice and fast. Someone gave me a 2wire 2701HG-B. so i hooked it up to test it out and the internet was honorably slow. Web pages would load if i was lucky. and i couldn't watch youtube. the internet seemed a tad faster wireless than hardwired. I changed everything back to my old router and modem. is there any settings i need to change to make the 2wire internet faster? anything will help. thanks
ive put together wireless networks with a modem and a wireless router before. with a fast speed. but the 2701HG-B is a modem router and a wireless router all in one. and i know how to secure a wireless network.