Modem problems

Hi there o/
Ive got a problem i would like some help with.
My ISP has recently upgraded my service to 8mbit instead of 0.5.
But i didnt get a new modem (the one i had supports 8mbit)
The modem is a SpeedTouch 510 with the newest firmware.
But since i recieved my new service, it has become unstable.
I constantly get this error message in the modem log:
-----------------------------------------------------------------
xDSL linestate down
PPP link down (PPPoE) [IP.TO.ISP]
xDSL linestate up (downstream: 8128 kbit/s, upstream: 960 kbit/s)
PPP PAP Authenticate Request sent
PPP PAP Authenticate Ack received
PPP link up (PPPoE) [IP.TO.ISP]
-----------------------------------------------------------------

My friend also has the same problem, and he does not live near the same telestation (40min away from it).
What i wanted to know, what might be causing this, is it the modem itself?
Or is it an external source?
I think its the modem...

Also, if you do believe it is the modem then i wouldnt mind some suggestions on good (available in sweden) modems for 8mbit+.

o7