Cable Forum - very poor wireless on wrt54g on dd-wrt...

hi all,
I've had to write this on my mobile phone as my ie freezes trying to access this forum for some reason.
Basically i've noticed this week that my wireless performance has been really poor...
I tested with 2 laptops in the same room as the router and would only get download speeds of about 700kb/s. The upload speed would often be better. I tested on speedtest.net, the speed test on here and at gamefiles.virginmedia.com. All really poor results.
If i connect directly to the modem i get about 18mb/s.
No other local wifi networks are on the same channel.
I did put the transmit power up to 70mw from the default of 28 recently. I'm worried it's burnt out or something?
Strange thing on netstumbler it shows the signal as single lines rather than a solid block if you know what i mean.
Should i get a new router do you think?
I was thinking about the gs one with speedbooster?

---------- Post added at 21:50 ---------- Previous post was at 21:05 ----------

Hmm...just disabled QoS and it's back to normal....well downloading at about 8mb/s on all speed tests...
I'm not sure the WRT54G does support 20MB on the WAN port? Even if I'm only about 2 feet from the router that's the best speed I can get on wireless...

---------- Post added at 22:10 ---------- Previous post was at 21:50 ----------

spoke too soon...
The speed's dropped right down again...about 1mb/s at the most, generally about 600kb/s...and I'm sitting right next to the router and rebooted it...
I'm thinking some sort of interference maybe????