There's a reason you see this in the mirror listing:
Code:
us http://mirrors1.kernel.org/slackware/
us http://mirrors2.kernel.org/slackware/
us http://mirrors3.kernel.org/slackware/
us http://mirrors4.kernel.org/slackware/
If you use mirrors.kernel.org as opposed to mirrors#.kernel.org, you'll get redirected to one of the four numbered mirrors (I don't know if it's location-driven or what, but that part's irrelevant for our purposes), and they're not always in sync with each other (syncing takes time).
