Download Speed Spikes Then Drops

I'm having a strange problem that I haven't been able to isolate with my internet speed. A couple days ago I did a system restore of Windows after finding a virus. I then noticed my bandwidth was considerably slower than the usual 10 Mbps (megabits not bytes). I then did a clean install after figuring that there was nothing else I could do. After reinstalling everything I noticed that the problem had not gone away. However, my laptop was not having any problem downloading games from Steam at the usual speed.
I did multiple tests at speedtest.net and the results have been all over the place. I've gotten everywhere from 3 Mbps to a short spurt of 14 Mbps. In multiple tests, I also noticed that I would spike up to around 10-12 Mbps and then drop back down to around 6 or so.
For a short amount of time this afternoon I also noticed that my download speeds in Steam were at around a normal level with very little variation. I would get speeds around 1.5 megabytes per second and occasional drops into 500 kb/s or so but nothing drastic. However, after a little while my speeds on my laptop also dropped to the low levels that I'm experiencing on my desktop. Now I'm seeing fluctuations where I'll have 1.3 MB/s and sudden drops into 500-600 KB/s when nothing else is using my bandwidth.
My current setup consists of a Motorola Surfboard Cable Modem connected to a cable splitter that also feeds into my television. From the modem I have an ethernet cable running into a Belkin N450 Wireless N+ router. From the router I have an ethernet cable plugged into the back of my desktop since I don't have a wireless card for it.
I currently have my 'Speed & Duplex' set to 100 Mbps Full Duplex as recommended in another thread I've found here but that doesn't seem to have done anything. My Windows Resource Monitor also isn't picking up anything using up the bandwidth on my network. I'm at a loss as to what to do next and my google-fu has failed to help me find a suitable fix for this problem.

I wasn't sure where to put this thread so if I should move it let me know. Here is the problem.
My dsl connection seems to not be working right with Steam. I'm trying to download a game and my connection which is a dsl 1.5mb, will spike at 200kbs then fall flat to 0kbs then back up. It keeps doing this and it's driving me crazy. I've tried tweaks. I've tried speed test and ping test. I've tried DSLreports tests with everything coming back ok. I've tried different and less busy Steam servers. I've tried changing DNS servers. I've tried turning off both of my firewalls. I've tried turning off my AV protection. I've ran deep scans for any kind of virus and found absolutely nothing. I've literally tried EVERYTHING. WTF is going on?