I'm using an Acer Aspire 5720G and iwl4965 network card.
After challenging this issue for days and hours, managed to how to fix it.
Solution is replacing default "network-manager" with "wicd". After doing this, my connection was full speed again!
This method also works with all LinuxMint and Ubuntu variants just like Kubuntu, elementary OS and all other Ubuntu based distros.
How to fix it?
- Open Terminal and type commands below.
- sudo apt-get install wicd
- sudo apt-get remove network-manager-gnome network-manager
- Open wicd from programs menu and connect your network.
- Enjoy full speed internet again on your Ubuntu!