Ok so I fixed  this by installing the 2012 driver from dell site. I had previously installed a 2014 driver from the realtek site.? I would have thought the later driver, which installed with no errors, was better. ???
My Dell Vostro Realtek PCIe GBE Family Controller will  not connect at gigabit speeds on our LAN. All other laptops will (broadcom adapters). Does anyone know how to get gigabit speeds?
Realtek PCIe GBE Family Controller