If your chain is skipping cogs on the cassette, usually in the highest gear, then don't always assume that a worn chain and cassette is the issue.
I usually find that when my chain starts skipping on the 11T cog, it's a dirt build up between the 11T and next cog that causes the issue. Compacted dirt sits in the space between cogs and causes the chain to ride up off the cog under power.
I use the serrated edge on one of these cheap tools to remove the crud. Best done with the rear wheel elevated, where you can spin it with the tool in between the cogs.
Kamasa Cycle Bike Motorbike Sprocket Cog Cassette Chain Claw Cleaner Brush
I usually find that when my chain starts skipping on the 11T cog, it's a dirt build up between the 11T and next cog that causes the issue. Compacted dirt sits in the space between cogs and causes the chain to ride up off the cog under power.
I use the serrated edge on one of these cheap tools to remove the crud. Best done with the rear wheel elevated, where you can spin it with the tool in between the cogs.
Kamasa Cycle Bike Motorbike Sprocket Cog Cassette Chain Claw Cleaner Brush