Not a speed complaint, but why was it so fast a few days ago?

[#1]

Hello, I've been a Plusnet customer for about a year or so and I've had a pretty rock solid 1.5mbps connection during that time. A few days ago, I noticed that my download speed had increased to around 2.5mbps (good enough to play Onlive!) which was great for a couple of days, then it fell back to 1.5mbps.
As I said, my connection is pretty solid, the speed doesn't fluctuate much and certainly has never increased by 1mbps.
My questions are, why did this happen, and if my line can support a 2.5mbps connection, why isn't it that speed all of the time?
Thanks in advance!

[#2]

Hi there,
I've just run a few checks against your line and can see that you currently have a line rate of 2315kbps, I can't see any obvious factors as to why you're getting only around 1.5kbps (if you still are). My advice would be to raise a fault here https://portal.plus.net/apps/kbdfaults
let me know if you have any difficulties after doing that.