Speed going down

[#1]

I was put on maxasdsl sometime back in 2007. Ever since then my speed has been consistently around 6246 kbps (781kB/s), 374 kbps (46.8kB/s), that is until this year when it initially dropped to 5613 kbps (702kB/s), 372 kbps (46.5kB/s) and is now down to 4291 kbps (536kB/s) 374 kbps (46.8kB/s). The upload speed has been consistent but the down load speed is ever decreasing.
The modem, filters and sockets all remain unchanged.
I believe that my exchange was upgraded this New Year to ADSL2+.
What is going on? has my speed decreased because of ADSL2+?

[#2]

Hi robalb,
I've just been checking and your profile is 7150. It was 6500 on our system, so I've matched that now. If you're still getting slower speeds then have a look here for some troubleshooting tips.
Jojo

[#3]

OK the only thing which has changed since my post was your reply Jojo.
Now the speed is today 6278 kbps (785kB/s)  379 kbps (47.4kB/s) - just as it should be.
You have worked magic already so soon.  
Download speed (kbps) Upload Speed (kbps) Date (YYYY-MM-DD) Time (hh:mm)
6246 374 20/11/2010 09:32
5890 372 14/02/2011 15:00
5613 372 03/03/2011 13:19
4064 374 19/04/2011 17:22
4505 380 20/04/2011 16:40
4311 380 20/04/2011 17:25
4291 374 20/04/2011 18:05
3063 371 21/04/2011 17:31
3090 370 21/04/2011 17:32
6278 379 22/04/2011 15:57