[Sephiroth]

It may seem a simple question to you, because you have the experience of your situation in your head. We, on the other hand, can only see what you write. So:

1 What is your daytime speed? (before 16:00)
2 How does it tail off - like getting worse through the evening?
3 What is your user experience? What is suffering?
4 Where are you located?
5 How is your PC connected to the cable modem?
6 When did this phenomenon start?

That's a starter list.

Speed fluctuates for one of three reasons, essentially:

1 Congestion / contention at your VM server node
2 Ditto on your trunk to the street cabinet
3 Circuit problems between your modem & the street box
4 Circuit problems at your VM server node due to poor load balancing

Cheers