Even though not relevant anymore, how much is your download from that site now?
I don't buy the problem was with modem, when SpeedTest was giving top speed. It is still good that you cleaned it, don't get me wrong. I just think your reasoning is wrong, and shouldn't base your judgement on a random download site. You can select a distant server (on the other part of the world) in Speedtest and it should still download at full speed with not so good ping values. Of course this depends on the server you connect to, however most servers should support your speed.
This is how I do it:
- If I sense any slow downs, I test with SpeedTest
- if it is indeed slow, I test with another SpeedTest server (sometimes servers need a restart :P)
- I also test with my laptop or phone (all smart phones have Speedtest apps) to rule out problem with computer
- if still slow, I reset my modem (it is a modem/router combo), when I had separate modem and router I used to reset them both. Then run another SpeedTest
- if still slow, I call my ISP's technical assistance service
- sometimes they re-apply some settings and all turn alright, sometimes it happens to be a regional problem (usually fixed in a couple of hours), if it is not fixed by any of these, ISP technicians come within 5 hours of my call and see if anything is wrong inside the home.
I hope this clears some confusion.