I already contacted Intuit support.  I've spent 10+ hours on the phone with them over the last 4 weeks. 

They all have the same checklist, which i've done multiple times:

• Verify / Rebuild
• Ensure no negative items
• Ensure system requirements are met on computer / server
• Move the location of the file
• Use different templates
• Ensure file size isn't too large
• Update QB to the most recent version
• Ensure Windows is up to date
• Try the same action with other users

Even Intuit's support team members admit that FIFO and Advanced Inventory isn't something they can support well.  

When I turn FIFO off, the transactions immediately speed up.  When I turn it back on, the same transaction CRAWLS.  Just changing the date of a sales order from September to November take 10 minutes.  But after I change it, I can invoice it like normal.  Sales orders written today work great.  

I can't delete some PO's either - IE - an open PO form July take 30+ minutes to delete.  Again - i turn FIFO off and the same PO deletes immediately.  

Its acting like FIFO is calculating for open sales orders and unreceived PO's.  Which makes no sense because FIFO should only be based on the date of the invoice and receipt of a PO right?