One thing I've noticed which I've never seen mentioned on this site is the issue of heat (I'm wondering if I'm going to open a can of worms, ah well)
One typical cause of problems is a hot router, All routers I've found to start behaving erraticaly or refuse to sync once ther'e too hot.
By placing your palm on your router: does if fell warm or hot to touch (as in the heat off a hot/warm cuppa)
If so is it sitting directly on carpet, if so then is the carpet warm under the router.
Is it sitting on top of another appliance producing heat.
Have you got something on top of the router, (paperwork books even a plate with toast on it)
Is it by a heat source like a radiator/ heater or a heater blowing warm air on it.
If it's just a little warm, thats normal. Say yes to any of the above then this may be something to look at and experiment with to see if you get any improvement.
Voyagers tend to be the hottest type in normal working conditions, the heat should feel at most in the corner where the power lead goes in. netgears seem to be the coolest. if you can having the router sitting on it's edge rather than flat can some times help. If the router still seems exccesivley hot, then try borrowing another router to see if you get a performance difference.