three page path. final answer was P12:P9:P6 with 7 occurrences.

gistfile1.txt

var fs = require('fs');
var _ = require('underscore');
var line, user, page;
var userPath = {};

fs.readFile('./input2.txt', 'utf8', function(err, data){
  if (err) throw err;
  var array = data.toString().split("\n");
  for (i in array){
    line = array[i].replace(/\s+/g,'').split(',');
    user = line[1];
    page = line[2];
    if (line[0]){
      if (!userPath[user]){
        userPath[user] = [page];
      } else {
        userPath[user].push(page);
      }
    }
  }
  processFile();
});

var processFile = function(){
  var finalPath = {};
  var threePath;
  _.each(userPath, function(value, key){
    for (var i = 0; i < value.length; i++){
      if (value[i-2]){
        threePath = value.slice(i-2, i+1).join(":");
        if (!finalPath[threePath]){
          finalPath[threePath] = 1;
        } else {
          finalPath[threePath]++;
        }
      }
    }
  });
  var maxPath, maxNum;
  for (var key in finalPath){
    if (!maxPath || finalPath[key] > maxNum){
      maxPath = key;
      maxNum = finalPath[key];
    }
  }
  console.log('final', maxPath, maxNum);
}