1400 feet is outside in perfect conditions, and even that is pretty rare on any router without some help.

Indoors every single wall or door will degrade the signal. What are you using to connect the Tivo to it? The original Tivo wifi adapter? AFAIK Tivo doesn't support any 802.11n adapters so the ".n" part of your router is useless to it and it'll be working in 802.11g mode.

Try changing the channel on the router, making sure there are no 2.4GHz phones anywhere near and making sure the router isn't hidden away. Try putting the router somewhere higher.

In the end you'd probably been better off with a simpler router with a good external antenna, like the Buffalo 54GSHP. 802.11n routers are nice for fast connections, but don't deliver the kind of range a good old 802.11g router with antenna can.

FWIW; most reviews of the N1 are pretty unanimous in confirming that the Belkin has poor range.

Can you still return it?