OK seems to be cable related, now isolate it. Test the lower section and FD, shifting by pulling the bare wire away from the down tube. If that's OK, either disconnect the wire from the FD, or hang the FD on the larger chainring, and work the lever against hand pressure on the bare wire. If that seem hard, something's wrong upstream, possibly a ferrule is misaligned, or the housing was cut badly and is trying to extrude through a ferrule or stop pinching the wire.

Lastly it could be something in the lever itself or how the wire is threaded into it. the sevret to working through these issues is to isolate areas until the problem is pinned down to one place.