You're getting wait states, or contention in your system. For a quick & dirty look at what's happening, query the DMV sys.dm_os_waiting_tasks while the suspended status is going on. That'll tell you what's blocking it.
"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood"
- Theodore Roosevelt
Author of:
SQL Server Execution Plans
SQL Server Query Performance Tuning