Linkysys WAG354G Router----Strange problem

[#1]

I don't know if this is a common problem with this model of router or this one is faulty.  After two days the download speed drops from the usual 4 to 6 Mbps to less than the upload speed, usually about 120 kbps, reboot it and the speed comes back to normal.
It does this every two days, can almost time it to the hour. The connection does'nt drop, sync rate stays the same and the noise margin stays steady as well, the speed justs drops.
I now switch the router off at night and back on in the morning as this happens everytime anyway. It's the latest firmware and I have a good line, normally syncs around 8000 kbps with a 12 db noise margin and it's interleaved. It's not over heating, barely warm to the touch.
Anybody any ideas about this one.
Ron

[#2]

I can't really say what the problem is but I too have this router and it has been absolutely fine since I first installed it 14 months ago (fingers crossed).
I never switch it off and as you say it runs warm but not hot.
My first router of this type had a fault (apparent as soon as I tried to install it) and upon telephoning the Linksys CS freephone number  the fault was confirmed, a number given and I returned it to the store and swapped it for another.
On the odd occasion that I have telephoned Linksys the staff were very helpful and polite. It might be worth giving them a call.
BTW I have never updated mine (not sure if I can) and it only has WEP encryption (yes, I know that the other one is better).
I daren't fiddle about with it because it works so well and I don't want to upset things.

[#3]

Thanks for the reply, this router is about 18 Months old now but this problem has been there for quite a while, can't even remember when it started.  Will try the Linksys CS  and see if they can come up with a solution.
The latest firmware is 1.01.58 by the way if you want to give it a try, but as you say if everything works why change it.
It's quite easy to change security to WPA Pre- Shared Key and much more secure. Just go into the settings
Wireless
Wireless security
WPA Pre-Shared Key
Enter password
Save settings
Do the same on the computer you are using and save settings again, thats it. There's a help page if needed. It's quite a good router to set up and change settings.
Ron

[#4]

You need to work out if the problem is with the router or your pc. When you get the problem does rebooting the pc fix it? Do you have any error messages in the event log like  Event ID 4226 you are limited to the number of connections you can run on XP sp2 and exceeding that would show up as the problem you are getting.
Over time updates etc can exceed this do you use p2p.  On you router try the page http://10.0.0.2/ADSLCStatus.htm change the 10.0.0.2 to your routers ip. Are you connecting with wireless or ethernet?
Next time try rebooting the pc ideal leave of for 2 mins.
If you are using cable try an other port.
Can you do a ping from the router and compare the response to the pc doing the same ping

[#5]

Never tried rebooting the PC, usually do a hard reboot from the router interface and this brings the speed back to normal.
Checked the event log and none of these error messages are showing, it is XP sp2 on both desktop and laptop. Desktop computer is ethernet, laptop is wireless. I don't use P2P at all.
The next time this should happen is tomorrow night, the router will have been up for near enough two days then, it usually happens when 
I'm using the laptop later at night, don't know if this has any relevance or not .  Wiil try some of your other suggestions the next time it happens. Apart from this problem the router works ok, it just wont hold the speed for any longer than two days.
Ron