Rendering data on gridpanel is very slow/ Extjs 4.2.1

I just updated my aplication from ext js 4.1 (Build Date 2012-07-04- 21:23:42) to extjs 4.2.1.883, but my gridpanels are rendering very slow, it took almost 30 seconds in rendering for each request. This is my code of my store:



Ext.define('App.store.Item', {

extend: 'Ext.data.Store',

requires: [

'App.model.Item'],

constructor: function(cfg) {

var me = this;

cfg = cfg || {};

me.callParent([Ext.apply({

model: 'App.model.Item',

remoteFilter: true,

remoteSort: true,

pageSize: 50,

proxy: {

type: 'ajax',

url: '/Item/GetItems',

reader: {

type: 'json',

messageProperty: 'success',

root: 'result',

totalProperty: 'totalCount'

}

},

listeners: {

'load': function(store, records, options) {

if (records) records.forEach(function(record) {

record.set('CreatedDate', Utils.parseJsonDateToDate(record.data.CreatedDate));

record.set('ModifiedDate', Utils.parseJsonDateToDate(record.data.ModifiedDate));

record.set('StartDate', Utils.parseJsonDateToDate(record.data.StartDate));

record.commit();

});

}

}

}, cfg)]);

}

});



With the previous extjs(4.1) it works normally. Now I realizes it is because I am doing some operation on load event to fix the format of date fields. But now I want it to work with the last version of extjs, How can I fix it? Any helps please.