Our 5.8 ghz phones knock the DSL modem off line whenever it rings or when it hangs up.l Before the call, during, and after, no problems at all.

Anything is possible.

When it's slow try putting the laptop next to the router, and see if it's still an issue or not. If it's not an issue, then it's probably interferrence in the signal, if it is still an issue, then it's probably the laptop or router.

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.