[Solved]-How can I force highcharts to show every x-axis label regardless of spacing constraints?-Highcharts

One solution is to use a tickPositioner function and specify every single index:

xAxis: {
    tickPositioner: function() {
        var result = [];
        for(i = 0; i < _mainData.length; i++)
            result.push(i);
        return result;
    }
}

See this JSFiddle example. You can remove xAxis.labels.step when using this.

At first tickInterval looks easier, but unfortunately doesn't work because of the following note:

If the tickInterval is too dense for labels to be drawn, Highcharts may remove ticks.