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Sorry you are having issues! You shouldn't need to do 100 percent infill. I'd recommend doing more shells (or outlines) for strength I doubt you should need more than 30% infill. By the way, Maker's Muse put out a good video on printing parts for strength: https://www.youtube.com/watch?v=1NzDr1YAb8Q

However, based on what you are saying, I bet your problem is due to the Z layers not bonding together. I would try raising your print head temperature by 5 C or more and see if that helps. If that doesn't help you may want to try a different filament. Good luck!