Best Excel library (for C#) and Issues Releasing Excel

1) Looking for an Excel library (open source) that is quick when adding rows to a spreadsheet. I tried using Microsoft.Office.Interop.Excel (Visual Studio 2012) to populate my spreadsheet and it's painfully slow (2 minutes to insert 3000 rows x 25 columns).

2) Issues releasing Excel ... despite releasing the object, I keep seeing Excel in my list of processes, sometimes multiple times. (FYI: Multiple users will be creating spreadsheets at the same time, so I can't kill all Excel processes)

3) The spreadsheet I am loading has multiple tabs with calculations ... can that be slowing down my process ? Prior to updating, I am setting Excel.XlCalculation.xlCalculationManual.

HERE IS MY SAMPLE CODE:

Application AppExcel = null;
Workbook ExcelBook = null;
Worksheet ExcelSheet = null;

try
{
    string ExcelPath = @"c:\temp\test.xlsx";

    //-------------------------------------
    // create excel object
    //-------------------------------------
    AppExcel = new Microsoft.Office.Interop.Excel.Application();
    AppExcel.Visible = false;
    AppExcel.DisplayAlerts = false;
    AppExcel.ScreenUpdating = false;

    //-------------------------------------
    // open Excel Workbook
    //-------------------------------------
    ExcelBook = AppExcel.Application.Workbooks.Open(ExcelPath);
    ExcelBook.Activate();
    int WorksheetToUpdate = 1;


    AppExcel.Calculation = Microsoft.Office.Interop.Excel.XlCalculation.xlCalculationManual;

    ExcelSheet = ExcelBook.Worksheets[WorksheetToUpdate];

    // test data
    for (int ExcelRow = 2; ExcelRow <= 3000; ExcelRow++)
    {                 
        ExcelSheet.Cells[ExcelRow, 1] = "Client #1"
        ...
        ExcelSheet.Cells[ExcelRow, 25] = "10020";

    }

    AppExcel.Calculation = Microsoft.Office.Interop.Excel.XlCalculation.xlCalculationAutomatic; 


    //-------------------------------------
    // save WorkBook
    //-------------------------------------                
    ExcelBook.Save();

    //-------------------------------------
    // release worksheet
    //------------------------------------- 
    Marshal.ReleaseComObject(ExcelSheet);

    //-------------------------------------
    // close WorkBook
    //-------------------------------------    
    ExcelBook.Close(true);
    Marshal.ReleaseComObject(ExcelBook);

    //-------------------------------------
    // quit Excel
    //-------------------------------------                
    AppExcel.Quit();
}
catch(Exception ex)
{}
finally
{
    Marshal.ReleaseComObject(AppExcel);
    GC.Collect();
    GC.WaitForPendingFinalizers();

    AppExcel = null;
    ExcelBook = null;
    ExcelSheet = null;
}