I have a 42 Fountain Lightning and the sliding cabin door is VERY hard to open. I have already set the dampener shock to the least resistance possible. Should I grease the sliders?

You might check the rail mount screws to see if they are loose & dragging on the slider,(happened to me) for lubrication you might try graphite. A dry lube as it will not attract dirt & grime. Randy

For sure check for loose screws, use blue Loctite to keep them tight.

Clean the track with a penetrating oil to remove any hardened grease/grime- that grit is probably the issue. My door slides best with clean dry rails.