I copied the bootx64.efi file from the EFI directory on the DVD drive, created a folder Slackware on /boot/efi/EFI, and copied the bootx64.efi
It also stops with Welcome to Grub.
Next what I am trying to do is either chroot and install grub or use my other distribution(s) to load Slackware
Update-
Slackware seems to have been detected
Code:
Found Slackware Linux (Slackware 14.1) on /dev/sda9