Progressively Slower Download Speed

Hello, I've been searching the forums as well as google for the past couple hours trying to find a solution to my problem and I can't find anything.

I recently reformatted my PC and upgraded the motherboard, ram, graphics card, and processor. Before reformatting I was getting good download speed around 10-12mbps (I'm supposed to be getting 20 but I have a relatively older USB wireless adapter and im a bit far away from the router) now after reformatting I've dropped to around 3mbps.

I've tried resetting the router, upgrading its firmware, resetting my adapter and upgrading its firmware and it's no fix. I have noticed if I unplug the adapter and plug it back in I'll get like 8-9mbps by the time I can run a test and if I run one right after it drops to 7 then 6 and finally stabilizes around 3 again.

All this time my upload speed stays right at 3-3.25mbps.

I'm out of ideas at this point, so any help is appreciated.