150 Mbps Connection Drops To 72 Mbps

I have a Netgear CG3100 modem hooked up to a Netgear WNR2000 router. Both are sending out signals, the CG3100 on channel 11 at 40 Mhz and the WNR2000 on channel 1 at 20/40 Mhz. I keep the WNR for legacy devices while the CG is for N devices only. They don't seem to interfere with each other much.Currently my computer is the only device connected to the modem wirelessly, with the only wired connection being the router. As I write this, the connection has actually dropped to 26 Mbps in the Wireless Network Connection Status window. I understand that this number drops under network load, but there doesn't seem to be any at the moment. If I go into the control panel and simply click apply, the connection jumps back up to 150 Mbps. However, this always drops back down, sometimes immediately, sometimes after a few minutes. It usually settles down at 72 Mbps, sometimes 54 Mbps.My wireless adapter is an ASUS PCE-N13 with v3.2.7.0 Ralink drivers. OS is Windows 7 64-bit.