This is not the first time that I heard of a performance issue after migrating from Access to SQL Server.
I would answer David's question because they are very important.
Placement of the mdb and the Servers is very important as was previously recommended.
Also if you see sp_prepare, sp_execute, sp_unprepare that is Access trying to execute a lot of individual queries and this results in a lot of network traffic. Access may execute sever individual queries for on Local Access Query and it does the processing on the workstation. I would recommend creating Stored Procedures and rather than creating views use in-line views or subqueries in your SP's
You can run the wizard to convert you tables but do you have the correct indexes. You should have a Primary Key Constraints on each Table. You should have FK Constraints and they should be Indexed to improve performance.
Make sure that you have to Clustered Index on the correct Column.
After you updating Statistics?
Are your mdb's stored on a Server or on each individual workstation?
If you have the time convert Local Access queries and extract SQL Code from behind the forms. Choose queries in which you get you Maximum Return on your Investment.
There is a lot more to do. When you migrated to SQL Server did you have a Development or at least a QA Environment?
If you can you may want to set up a Test environment so that it makes it easier to identify problems.
Are you using SQL Server or Windows Authentication?
For better, quicker answers on T-SQL questions, click on the following... http://www.sqlservercentral.com/articles/Best+Practices/61537/
For better answers on performance questions, click on the following... http://www.sqlservercentral.com/articles/SQLServerCentral/66909/