SW 2009 4.1 perfomance SLOW

The performance still is worse than 2009 2.0. Now whenever I isolate parts on a large assembly to work on them , after I am finished and return to the full model, some of the assemblies are way out of place. Why? All the parts are fully defined. This gets really annoying. Also the longer I work in SW the slower it gets even with the 3gb switch. I have more issues but looking to address these first. Please any advice would definately be appreciated. SolidworksAdministration