The CubCrafters XCub you have to use in this bush trip really struggles to climb over 11000 feet, going above puts the speed in the red and leads to stalling. In order to get to the Matterhorn in the third leg you need to be at 12000 or fly a massive detour to avoid the huge mountain range on the w…

It’s ceiling is 14,000 ft in the game. You may have to lean out your fuel mixture ratio. You can also map, “Set Best Mixture” in MSFS.