For me, setting up the video resolution has been a hazard area for most distros - and I try them all.
I never tried a Slack-based system before. Vector has promise, but obstinately, and with a will, refuses to believe that I have a 1600 x 1200 monitor capable of running all lesser modes, and a graphics card capable, and a /etc/X11/xorg.conf that is apparently correct. Yes - we do try all ways available to set up X, and the number of xorg.conf attempts by various methods is now up to generation 4.
Starting the X server with 'startx' is a frustrating series of reboots if the screen hangs. There are various X-config tools, but any that try to replace the entire xorg.conf (such as an adventure with KDE's system -> NVIDIA X Server Settings) can come unstuck. I tried it, and ended up needing to use a liveCD to rename the xorg.conf.backup, so as to get back to any screen at all.
The KDE -> Control Center -> Peripherals -> Display setup window is not the place! Reboots do not seem to update the KDE idea of the available resolutions. No matter what I do, there is something in a script somewhere that will have it the way it was before we started.
Maybe I am just not very good at this, and from the documentation, I can appreciate how there are a million ways of making the muddle worse, but I just want to use the machine to display and work on the digital art, not spend ages reading FAQs that lead to boot time lockups.