From the perspective today. You should not work rename your 8192cu.conf to rtl8192cu.conf because it is blacklisted on dist Linux 4.14.72-v7+ due to driver problems. Even the other informations above won't work for me.
If you want to confirm it by urself just look...
ls -a /etc/modprobe.d/
You will see "blacklist-rtl8192.cu.conf"
You can try this. It helped me with my bad connection and i'm on a fresh installed raspbian light with linux latest dist 4.14.72-v7+
sudo iwconfig wlan0 channel auto
sudo iwconfig wlan0 power off
sudo iwconfig wlan0 txpower auto
sudo iwconfig wlan0 rate auto
sudo iwconfig wlan0 rts 2304
sudo iwconfig wlan0 frag 2304
sudo iwconfig that all settings applied.
rts and frag can b set 0 - 2347 and represents bytes. You can play with this values and look what fits best for you.
The problem ist that you have to restart your wlan after that and after reboot your settings get lost. So put them into startup properly to start them with your system.
sudo nano /etc/rc.local
paste above the stuff before exit 0 and don't forget to save!
Last but not least. Your HDMI Cable can make you hard times also. Don't use cheap cables because the signals will be interrupted from the wlan. Even hardmetal cases and +48v phantom sound stuff can interrupt your wifin con on pie. (my cable made me hard times and i read about it in the raspbian forums)
The script will be lost every time after restart. You should build a bashscript or start up script to load it on start (Follow link for more infos on that):Execute script on start-up