Why can't I get my SharePoint custom workflow activity DLL to update?

I have created a custom activity that I am using in my workflows. Initially changes that I made were picked up right away. Now for some reason it keeps running with an old version of the DLL. Is this cached somewhere? I have tried the following:

• update-spsolution -identity copy_special.wsp -literalpath c:\temp\copy_special.ws开发者_JAVA技巧p -GACDeployment (I think this reboots the app pool in IIS)
• Manually recycling the app pool in IIS
• canceling all instances of the workflow on sharepoint, uninstalling the workflow, updating the solution, then installing all over again
• Deleting cached files for SharePoint Developer on my local machine
• REBOOTING THE SERVER!

I have confirmed that the updated version of the DLL is in the GAC. I'm about to loose it here. Is there something else I should try? Is there a location that this DLL might be cached?

These are steps for the 2007 version of SharePoint Designer but maybe they are the same for 2010?

Try clearing the WebsiteCache on the computer that has SharePoint Designer installed:

For Windows XP or Windows Server 2003: Delete all directories and files at %System Drive%\Documents and Settings\%user%\Local Settings\Application Data\Microsoft\WebSiteCache

For Windows Vista or Windows Server 2008: Delete all directories and files at %System Drive%\Users\%user%\AppData\Local\Microsoft\WebSiteCache

http://social.msdn.microsoft.com/Forums/en/sharepointworkflow/thread/34632798-6e45-4eb3-ad3d-2f941c706cda

Turns out this was caused by user error. When I rebuilt my project in VS 2010 I assumed it was updating the WSP. It was not... It only updated the DLLs. I went ahead and redeployed it to my dev environment, THEN grabed the WSP and it finally updated. PEBCAK!