When a partition type of vfat is mounted, the system will mask the full permision set 777 with the umask setting, thus producing the the permisions for the mount point. So the umask is an inverse of the desired settings. For example; full permisions are rwxrwxrwx or 777. If you desire, rwxr--r-- or 744, then a umask of 033 would be correct. For rwxr-xr-x or 755, a umask of 022 would be correct. Notice the numbers will add up to 7 in each column.
Now for the problem or change in Slack 9.0. The system default umask setting is 022 and that is set in /etc/profile. This setting has not changed. However, the mount command has been modified to include some new options, fmask and dmask, and in the process the system umask setting is not being used. The mount command is defaulting to a umask setting of 033, producing 744 permisions (rwxr--r--). Even if the default umask is set to 000, it continues to use a 033 setting. However, if you force the command by providing the option for the umask setting then it will use it properly.
To manually mount with rwxr-xr-x;
mount -t vfat -o umask=022 /dev/hd?? /mnt/point
To mount from /etc/fstab with rwxrwxrwx;
/dev/hd?? /mnt/point vfat defaults,umask=000 0 0