ASP.Net List View becomes too slow when we load or update bulk of records. How can we improve its speed or any other alternative?

Question

I'm trying to load and bind records with ListView but i'm facing these two issues

1. It is taking long time to load the records
2. When i save records after update, it gives error Maximum request length exceeded.

Below is the first method which calls on button click.

private void LoadItems()
        {
            string warehouseCode = txtWarehouseCode.Text;

            if (string.IsNullOrEmpty(warehouseCode))
            {
                ShowMessage(GetLocalResourceObject("1208").ToString(), Messages.Red);
                return;
            }
            DataTable dt = invManager.ItemCardStockManager.SelectOpeningStock(warehouseCode);
            lsvItems.DataSource = dt;
            lsvItems.DataBind();
        }

And here is the ItemDataBound method which calls during binding.

protected void lsvItem_ItemDataBound(object sender, ListViewItemEventArgs e)
        {
            if (e.Item.ItemType == ListViewItemType.DataItem)
            {
                HiddenField hdnHigherUnitQty = e.Item.FindControl("hdnHigherUnitQty") as HiddenField;
                HiddenField hdnBaseUnitQty = e.Item.FindControl("hdnBaseUnitQty") as HiddenField;
                HiddenField hdnOpeningCostPrice = e.Item.FindControl("hdnOpeningCostPrice") as HiddenField;
                HiddenField hdnUnitFraction = e.Item.FindControl("hdnUnitFraction") as HiddenField;
                HiddenField hdnHigherUnitType = e.Item.FindControl("hdnHigherUnitType") as HiddenField;

                decimal uq1 = (hdnHigherUnitQty.Value == "" ? decimal.Parse("0") : decimal.Parse(hdnHigherUnitQty.Value));
                decimal uq2 = (hdnBaseUnitQty.Value == "" ? decimal.Parse("0") : decimal.Parse(hdnBaseUnitQty.Value));
                decimal cst = (hdnOpeningCostPrice.Value == "" ? decimal.Parse("0") : decimal.Parse(hdnOpeningCostPrice.Value));
                decimal fr2 = (hdnUnitFraction.Value == "" ? decimal.Parse("0") : decimal.Parse(hdnUnitFraction.Value));
                int ut2 = (hdnHigherUnitType.Value == "" ? int.Parse("0") : int.Parse(hdnHigherUnitType.Value));

                TextBox lbHigherUnitQty = e.Item.FindControl("lbHigherUnitQty") as TextBox;
                TextBox lbBaseUnitQty = e.Item.FindControl("lbBaseUnitQty") as TextBox;
                TextBox lbOpeningCostPrice = e.Item.FindControl("lbOpeningCostPrice") as TextBox;
                TextBox lbUnitFraction = e.Item.FindControl("lbUnitFraction") as TextBox;
                TextBox lbHigherUnitType = e.Item.FindControl("lbHigherUnitType") as TextBox;

                lbHigherUnitQty.Text = uq1.ToString();
                lbBaseUnitQty.Text = uq2.ToString();
                lbOpeningCostPrice.Text = cst.ToString();
                lbUnitFraction.Text = fr2.ToString();
                lbHigherUnitType.Text = ut2.ToString();

            }
        }