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Kyrieknight Rip I was halfway through typing something up for Alolan Sandslash before I went back and read you said Let's Go Pikachu
Your moveset is pretty good already! I'd say switch Drill Run out for something better because it's pretty much just a weaker version of Earthquake. Gyro Ball is a good choice, because Sandslash isn't very fast and it has decent attack.
Super Fang is another one, it cuts your opponent's HP in half. It's base physical attack is 100 while its special attack is only 45, so stick to physical moves.
Also Stone Edge or Night Slash for coverage.
My last suggestion is Rapid Spin, it gets rid of any hazards on the stage like spikes or stealth rock, and raises speed by 1. Sandslash's speed is only 65, so it needs all the speed it can get.
Hope that helps!