Zack,
When you stop the ADAudit Plus service, does the performance increase?
If so, my guess is a credential issue is wrong on the tool.
Otherwise, might be an issue with contacting all of the DCs, might do a ping of all DCs from the box where ADAudit Plus is running.
Finally, 8GB for a Windows Server is not all that much. Is this server performing other duties other than ADAudit Plus? Might want to bring up the Task Manager and look at the apps/resources eating up most of the memory or network.
Derek