If you enjoyed learning Master of Puppets and you're looking for something similar I'd recommend checking out Blackened if you haven't yet. Like Master of Puppets it's one hell of a down picking workout. It's a hair easier but it's still a challenge. I started working on The Sentinel by Judas Priest a while ago and kind of put it down after a little while because I ended up working on the rhythm section to Painkiller instead. I've been slowly but surely working on the main riff to Amon Amarth's Twilight of the Thunder God for a short time now. Not very dedicated to it but it has got me working on my string skipping anyway. It's harder than it sounds which caught me off guard initially haha. Anyway I hope this gives you some ideas. Hope you're doing well man!