Downloading is sporadic through clearwire router

I just got a new router and hooked it into my Clearwire modem. Now, I have a second computer downstairs hooked into the router via Ethernet cord. Everything browses perfectly and rapidly (Special thanks to firefox boosts (Yay pipleline)).

However, downloading is very stop and go, and often will cruise at about 800kbps and then stop. It’ll sometimes go to 10% and stop, claiming to be going at some speed, other times it will go to 90% and do the same thing.

Sometimes it doesn’t even start, and remains at 0. Only if I try 10 times in a row and get lucky does it finish the download.

Is there any simple solution to this?