• The reason I asked about big/small is that the newer stuff won't let you use small front ring with two smallest cogs at the back. So, if it's in the small cog, put the chainring into big and try again. It should shift up to the 3rd cog at the back but perhaps it's struggling to move 3 steps at once - again I'd look for loose mount, crooked mount, b-screw not seated properly, twisted anything, etc.

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