Latitude 5440 performance issues

I hope someone can help assist.  Our IT department has seen an increase in calls about the Latitude 5440.  Our users are reporting that it can take up to 20 min. to go from power on to being able to sign into Outlook.  We noticed that it was also taking a long time to connect to our wireless network. We have done the following to troubleshoot the device and believe that it may be a driver issue:

• Ran pre-boot diagnostics 
• Imaged the devices using SCCM
• Imaged the devices using the OEM
• Updated all drivers and flashed BIOS
• Removed all non Microsoft and Dell processes from startup
• Disabled wireless to see if the results were the same when on a wired network, they were.
• Logged in as a different user to duplicate the issue. 
• Restarted the device in safe mode, where we did not experience any issues with booting and connecting to the network. (This is why we believe that it may be a driver issue.) 

If someone knows what the issue could be or how to test if it is a bad driver, please let me know.

Thanks,

Tom