Performance Difference Between Query Executed Through ASP.NET And SSMS

I have also posted this in microsoft.public.sqlserver.programming.

I have a query which, depending on where I run it from, will either take 10 milliseconds or 10 seconds.

The query works perfectly when run in SQL Server Management Studio... in my database of around 70,000 items it returns the results in around 10ms. It uses all my indexes and indexed views correctly.

However when I run the identical query from my ASP.NET application, it takes around 10 seconds... 1000 times longer.
Looking at it in Sql Server Profiler I can't see any difference in the query, except from ASP.NET it needs 62531 reads and from SSMS it needs only 318 reads. If I copy the slow running ASP.NET query from the profiler into SSMS, then it runs quick again. The results returned are the same.

I have provided more details of the query below, but I guess my real question is: What is the best way to debug this? I'm not an expert with SQL Server, so any pointers on where I should start looking to find the difference in how the query is being executed would be a great help.

The query is of the form:

WITH RowPost AS
(
SELECT
ROW_NUMBER() OVER(ORDER BY DateCreated DESC) AS Row,
ItemId,
Title,
....
FROM
Items_View WITH(NOEXPAND)
WHERE ItemX >= @minX AND ItemX <= @maxX AND ItemY >= @minY AND ItemY <= @maxY
)
SELECT
*,
(SELECT Count(*) FROM RowPost) AS [Count]
FROM RowPost
WHERE Row >= @minRow AND Row < @maxRow

Where Items_View is an indexed view, and WITH(NOEXPAND) is being used to force it to use the indexed view (this is optimal). The line beginning "SELECT Count(*)" is to get the total number of results (without having to run the inner query a second time).

This is running against SQL Server Developer Edition.