pkgtool works fine here. Try downloading the package again and verifying it (gpg and/or md5sum). Then upgrade it with
Code:
# upgradepkg --reinstall pkgtools-11.0.0-i486-4
Edit: It dawned on me that if pkgtool is broken, then upgradepkg might be broken as well. If the above doesn't work and you have a slackware boot disk then boot with it. Mount your root drive on /mnt (or whatever), then upgrade the package with
Code:
# ROOT=/mnt upgradepkg --reinstall pkgtools-11.0.0.i486-4