I've searched through the forums and the web to no avail, hopefully somone can help.

I'm using LinuxMint and it finds and connects to my n900 with no problems. Initially, my connection will run at anywhere from 50-100 kbps. Within minutes or, more often, seconds, the connection will begin to slow down dramatically until it stops altogether. The network manager still shows connected, and the n900 doesn't have any issues getting to the internet.

I've tried different network managers (wicd, wvdial, ceni) and different settings, nothing seems to change it.

Any help is appreciated.

While it sounds counterintuitive, disconnect the phone from the internet first. This will free up the GPRS modem completely to be used by the tethering client. Also, make sure the search interval is set to 0 to avoid the modem dialing out again while you are tethered

This also seems to improve tethering over bluetooth as well.

See here:
http://dartarrow.net/using-nokia-n900-as-a-modem/137

Are you using the power kernel? I have heard there are slowdown issues with tethering with that.

Yeah, I've tried disconnecting from the internet first. I was actually surprised to see the computer would reach the internet when the phone was not connected to the internet. Also, I was using the power kernel, and just tried this morning to connect without it and there was no change in performance. Search interval is set to never. I've tried the setting in the link you provided and had no luck there either.

It could be the power kernel, then. I had experienced the same slowdown after installing the package myself awhile ago. Then one night, I screwed something up and had to flash the firmware. I can use bluetooth DUN fine again and haven't re-installed power kernel since. I think there are some threads about this issue here on the forums.

Here is the thread I remember seeing about the Titan kernel slowing tethering down:
http://talk.maemo.org/showthread.php?t=56261

I am trying titan's power kernel version 2.6.28-maemo37 and it seems to work okay with tethering. I am in the car now and getting 1 mbps download.

nice, I'll give it a try. thanks for the replies.