Monitor recommended 1280x1024 85khz (no vibrating or flickering in Slack, but anything higher it vibrates)
H 30-96 khz
V 48-179 khz

I've used 1600x1200 in SuSE, Red Hat and Windows with no problems; however, in Slackware the refresh rate goes way over.

If I change my resolution to 1600x1200, the refresh rate is at 93.7/75hz so the display is vibrating and flickering back and forth. How do I set it to go only at 75 instead of way over 75. I've read something about xvidtune, but adding that to XF86Config gave "no screens found".

Right now I'm using 1280x1024 and my monitor status says the refresh is at 91.1/85 with no display problems, but I'd like to use something higher on this 19 inch in Slack.

You run it and it configures XF86Config

I run what?

I was talking about xvidtune. You can also configure the monitor with xf86cfg. They are both programs that make it easier to configure X.