Originally Posted by
jccaclimber
This is my first guess. Worn rear cassette is on the list as well.
A picture and video would help.
Does it do it shifting high to low as well as low to high, or in just one direction?
Did you read the first post? OP says it happens every other cog. Can't be the chain routed incorrectly if he is indeed telling the truth about when it happens.