Originally Posted by chadsrepair

Remove the derailleur cable and try to shift, if it moves freely then reinstall the cable without wrapping it over the top. Go from the bottom and make it a down pull instead of a top pull. When in #1, the cable should not be tight, there should be a little looseness. Try rerouting the cable first, I’ve found this to be an issue on many bikes; you’re essentially making it an up pull vs down pull. That should work.