Originally Posted by cordelli
It could also be what you are sending, the initial login is short, fast, and bursty, so it could be coming that fast. Surfing is long packets that come and go from the router, and it may have something to do with how fast the stuff is coming in off the internet. If you are for example running DSL or a slower cable, you can't possibly hold the 54 speed, because the router can't get packets back and will slow down.
I think you're talking about throughput and not the negotiated wireless speed. The negotiated speed of the transport should stay at 54 or a relatively high number with excellent signal strength regardless of the throughput you're getting from your external connection. The wireless speed and signal strength doesn't vary based on the speed or length of incoming or outgoing packets to the external connection.
If it's going down to 2Mb, then you're getting some sort of interference. Just try moving it around a bit to try to determine if it's those steel shelves or not.
-David