TransactionScope locks table in SQL Server

Hello,

I need a little help with a big problem.
In my application I need open a Transaction to SQL Server 2005 and call a stored procedure that returns a result set.
But executing some stored procedures in a TransactionScope block, do the execution of these stored  procedures waste a lot of time to return. And without it, runs normally and fast.

Actually I have this environment:

- .Net Framework 4.0
- Microsoft SQL Server 2005
- SQL Server Isolation Level = Read Committed
- "TransactionScopeOption = RequiresNew"
- "IsolationLevel = ReadUncommitted"

What happens with this transactions?

Sorry my english, Thanks!