If it took two hands just after installation, and has gotten "better" but never "right", I'd suspect that it was kinked during the installation and that you're still fighting some kind of bend or crimp in the cable. You may have adjusted the cable so that neutral and reverse don't align the bend in the inner cable with the bend in the sheath, but when you go forward you have to push the bend past the sticky point.
Recommend checking the entire length of the cable run for any sharp bends. If you've got one, replace the cable (again.)
BTG