speed issue with wrt54n and 5100 card

i recently moved. i was getting 135mbps at the old place. plugged in with same settings here and getting between 18 and 40. only difference is i'm currently on a dsl "basic" which is quite a bit slower than standard comcast speeds. it's the package below "dsl elite" which is right up there with comcast. would that have anything to do with this?

wireless settings:



no convenient screenshot to see my 5100 settings as you have to click one by one to see what they're set at, but i followed a thread i saw here and as i said have not changed anything from when i was getting much more ideal speeds.

 

What speeds are we talking about?
This 135mbps and "between 18 and 40" are actual internet speeds (real life or speedtests) or LAN to LAN transfers or maybe it's the speed you are connected to your router?
You need to clarify that because at this point I have no way of knowing if speed was measured by speedtest and is lower because your comcast connection is slower, or you test it internally (LAN to LAN) and we’re talking WiFi settings here (overcrowded channels and so on)

 

135mbps was the speed my router was getting from my wireless laptop before i moved, 27mbps to 40mbps is what i'm getting now on the same settings. there's no other connections to the router other than one desktop that barely gets used.

 

If other networks in the area may be dropping it down. 11n requires it to play nice with other networks, meaning it may fall out of wide mode.

 

the fact that it's WPA2 protected doesn't change that? i'd like to at least temporarily be able to get my old standard "54mbps" that my wrt54g gave me for years and years.

 

WPA2 has nothing to do with it. It's not that someone is using your connection but that there may be other wireless networks running on the same channel as yours (or neighbouring ones that are overlapping)
I'd recommend you run an app called inSSIDer to scan for other networks and choose a channel that's not being used or is used by some network with very low signal strength (if no channels are free)
Preferable channels are 1, 6 and 11 (in the US) and 1, 5, 9 and 13 in Europe as these are not overlapping but if there are networks with strong signals on these go for anything that’s free.

Link to inSSIDer (freeware) http://www.metageek.net/products/inssider

 

here's a screenshot: http://gyazo.com/1574e267685e1a7dbcd0b3a410079ea1.png

it says my speed is "65" on that, but it says 12mbps when i go to my network connections > wireless network connection. i'm also apparently the only one on my channel.

 

You did a scan of 5GHz freq. Why not add one for 2.4GHz?
BTW What router is it? There is no WRT54n as far as I know.

 

WRT160N. when i tried 2.4ghz i was getting the same results.

 

Problem doesn't seem to be caused by i.e. distance from the router to your laptop. In that case signal would have been week but at a constant level, whereas in your case it signal strength varies a lot.
It may be caused by interference with other devices such as wireless phones or bluetooth devices.
I'd also check two things- first- your 5100 card is N-capable and so is your router. If there are no legacy (b/g) devices on your network there is no need to use "mixed mode"- you may set your router to "n-only".
Second thing- the cause of interference may be sth that cannot be detected by inSSIDer like bluetooth or your neighbour's wireless phone so I'd start with putting your router radio band in 20MHz mode and that trying every single channel with inSSIDer enabled. Hopefully there are some channels that are not affected by whatever is interfering and you would see it immediately on the graph. Than you can get back to 40MHz band keeping in mind that both channels you use should give you good reception on their own.
You can always try to move your router a bit or put it a bit higher that the laptop is.