I bought a mid 2010 mac pro with a quad core Xeon processor from the original owner. i really love the speed of this machine compared to my MacBook Pro and iMac. I upgraded the GPU to a Radeon RX 580 as Apple recommended to run Mojave. Upgrade went smoothly. Now updates and downloads through the app store don't work. They just continue to run without results. I don't know if this coincided with the GPU placement or not but I can't think of how to fix this. I rebooted after deleting Pages since it wouldn't update. Now I can't even download a new copy much less purchase new apps. If anyone has any ideas or has dealt with this before I would appreciate the help. Thanks, Richard