What follows is info gleaned from a historical post with similar problems to your own, but answered by a true wireless guru. I am only regurgitating his knowledge:
iwlwifi (your driver) appears to have two issues in some laptops:
1. n-mode connection, and
2. conflict with bluetooth.
We can test if either solution works by:
1. Disabling n-mode with:
which you've already tried, or
sudo rmmod iwlwifi && sudo modprobe iwlwifi 11n_disable=1
2. Disabling bluetooth
sudo rmmod iwlwifi && sudo modprobe iwlwifi bt_coex_active=0
3. As guru @chili555 notes, you can try both with:
4. If either of these kludges work for you, you can make them permanent by doing:
sudo rmmod iwlwifi && sudo modprobe iwlwifi 11n_disable=1 bt_coex_active=0
and adding either "options iwlwifi 11n_disable=1" or "options iwlwifi bt_coex_active=0" or both to the file.
gksudo gedit /etc/modprobe.d/iwlwifi.conf
5. Even if this works, I'm not really happy with it as a real solution because it is a kludge that nerfs some functionality in order to work around a problem. If you are feeling especially brave or foolhardy, you may wish to install a newer iwlwifi module to see if that makes any difference. If you want to try a newer driver, open synaptic and search for the package name of your driver:This should give you a number of packages containing different versions of iwlwifi drivers. Carefully note the full names of all the checkmarked boxes and record them so that you know which is your current driver should you need to revert. Go through the list, compare, and choose one with a higher version number. Be careful that you are not installing the wrong driver for your architecture. amd-64 will not work with i86 and vice versa. You will also have to comment out the options in step 4 above in order to properly test the new driver.
If you feel that you can live with reduced functions (assuming any of the kludges actually work), you may wish to skip step 5 as unnecessary and just tempting fate.
Last but not least, read through the whole thread referenced earlier to see if any of the problems therein reflect your own and paying especial attention to the posts of @chili555. The above suggestions are derived from that thread.