SQL won't release memory unless the OS is under memory pressure. That's normal and that's how it works.
With 8GB on an x64 server you should set max memory no higher than 6GB. Disable AWE, it is not used on x64.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability