stored procedure taking almost 60 sec to excute

USE [xxx]
GO
/****** Object:  StoredProcedure [dbo].[Reports.Stock.StockSummary]    Script Date: 07/20/2012 12:31:30 ******/
--SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO


ALTER proc [dbo].[Reports.Stock.StockSummary]
(
	@StartDate as date,
	@EndDate as date,
	@DistributorUserID varchar(50)

)
as

declare @sqlStatement as nvarchar(max);
declare @sqlCondition as nvarchar (max);
set @sqlStatement ='';
set @sqlCondition ='';
set @sqlCondition = '';

SELECT  DISTINCT Products.ProductCode, Products.Description As ProductName, 
dbo.[GetOpeningStock](Products.ProductID,@StartDate,@DistributorUserID) OpeningStock,
dbo.GetIssuesBySalesMan(@StartDate,@EndDate,@DistributorUserID,Products.ProductID) As Issues,
dbo.GetAdjustmentBySalesMan(@StartDate,@EndDate,@DistributorUserID,Products.ProductID) As Adjustment, 
dbo.GetOpeningStock(Products.ProductID,@StartDate,@DistributorUserID) 
+ dbo.GetIssuesBySalesMan(@StartDate,@EndDate,@DistributorUserID,Products.ProductID) 
+ dbo.GetAdjustmentBySalesMan(@StartDate,@EndDate,@DistributorUserID,Products.ProductID) As IssuesTotal,
dbo.GetSaleQuantityBySalesMan(@StartDate,@EndDate,@DistributorUserID,Products.ProductID) As Sales, 
dbo.GetFocQuantityBySalesMan(@StartDate,@EndDate,@DistributorUserID,Products.ProductID) As FOC,
0 as Transfers, 0 as Replacement,
dbo.GetSaleQuantityBySalesMan(@StartDate,@EndDate,@DistributorUserID,Products.ProductID) + dbo.GetFocQuantityBySalesMan(@StartDate,@EndDate,@DistributorUserID,Products.ProductID) As TotalDisposal,
--dbo.[GetClosingStock](Products.ProductID,@StartDate,@EndDate,@DistributorUserID) as CurrentStock
(dbo.GetOpeningStock(Products.ProductID,@StartDate,@DistributorUserID) 
+ dbo.GetIssuesBySalesMan(@StartDate,@EndDate,@DistributorUserID,Products.ProductID) 
+ dbo.GetAdjustmentBySalesMan(@StartDate,@EndDate,@DistributorUserID,Products.ProductID)-
dbo.GetSaleQuantityBySalesMan(@StartDate,@EndDate,@DistributorUserID,Products.ProductID) + 
dbo.GetFocQuantityBySalesMan(@StartDate,@EndDate,@DistributorUserID,Products.ProductID)) as CurrentStock
FROM Products join StockHistory on StockHistory.ProductCode = Products.ProductCode
WHERE  StockHistory.OpeningStock > 0
AND StockHistory.DistributorUserID = @DistributorUserID


--set @sqlStatement = @sqlStatement + @sqlCondition;
--print @sqlStatement;
--EXEC sp_executesql @sqlStatement