Re: B3 shift cable
When you push the neutral button, it's throttle only and doesn't shift.
Disconnect the helm cable from the engine shift plate. Have someone hold resistance to movement of the cable and move the shifter. If it's still stiff, then you need a new cable. If you can't notice the resistance, the problem is either the lower shift cable or the drive.
Pull the drive and move the shift cable, it should move very easily. If it takes more than 1 finger and thumb with light pressure to move the cable, replace it.