How to fix Thunderbolt to Gigabit Ethernet slower than Wi-Fi Macbook Pro?

I recently bought a Thunderbolt to Gigabit Ethernet adapter so I could have faster Internet. I plugged the cable into my Internet modem, and the other end into my adapter. I plugged the adapter into one of my Thunderbolt ports on my Macbook Pro running OSX 10.11.3 El Capitan. The computer recognized it and connected to Ethernet. When I used speedtest.net, my WiFi had a lower ping and higher upload and download speeds than my Ethernet. I tried the cable to both Thunderbolt ports, all the ports on my modem, and my router, and even tried using a different Ethernet cable; it just wouldn't go faster on Ethernet.

I tried resetting my PRAM (Which has recently been changed to NVRAM, but is essentially the same thing), and deleting my Thunderbolt Ethernet setup in System Preferences. If you want to know;

Ethernet:

• Ping=17 ms
• Download=3.50 MB/s
• upload=1.21 MB/s

Wi-Fi:

• Ping=13 ms
• Download=3.76 MB/s
• Upload=2.19 MB/s

As you can see, my WiFi is not very good so I got the adapter to speed up my connection by using Ethernet. I just spent $30 so please if anyone can help I really need it.

I think there is something going on with El Capitan and a most recent update... My ethernet speeds (same network as an old Mac Mini) are 50x more (very seriously) than my iMac 5k. I get about 70Mb/s on the old Mac Mini and only about 1.5-2Mb/s on the iMac. I checked the network traffic, I checked the processing in the background ... nothing. That's changed recently (with nothing else changing) and I think it was due to an update. Frustrating though.