OK, let's start here - let's get the fragmentation level of your tables/indexes.

Go ahead and run this code.....

Note at the bottom I put a where condition on - to get the frag levels for a single table. So you can filter on a table, or just omit the where clause and get the frag level for all tables.

Let me know the column values for the table(s) in question. Anything over about 30% means the table should be reindexed, and anything well over 50% can definitely be an indicator of sluggish performance. If all the numbers on your major tables are under 30% then the problem is likely elsewhere.

SELECT OBJECT_NAME([OBJECT_ID])  AS TableName,   
       avg_fragmentation_in_percent AS Fragmentation,
       fragment_count, page_count
       FROM sys.dm_db_index_physical_stats
            (DB_ID(), null, null, null, null)
            where OBJECT_NAME([OBJECT_ID]) = 'PurchaseOrderHeader'