I could do with some advice please, i have a problem with my chain. When i am in a gear usually middle of cassette to bottom the chain slips occasionally especially when i put bit of power into the pedals. It is not when i change gear and i generally set my self up in the right gear if i am starting on a climb etc. Also i rotate two chains normally and clean them after each ride and then re-lube them when i put them back on the bike.
Any ideas???

