Only thing I noticed is that for every restart, I need to disconnect the eGPU. It works with hotswap connection only. (Updated 8/4/2019 - I plugged the TB2 cable to one of the bottom 2 slots on the Mac Pro Late 2013 and I no longer have to unplug the eGPU during restart/reboot.
(Update 8/13/2019 - OS X did an automatic update and it actually asked to run the PureWrangler script on restart. I ran it but noticed that eGPU is not being detected. So I removed all accessories off USB and restarted in Recovery mode (CMD-r) and did "csrutil disable" then restarted. The script was already executed so the eGPU got detected and is working once more. Thought I would give anyone interested a heads up).
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System Specs:
Late 2013 Mac Pro - Quad Core 3.7 / Radeon Fire Pro D300 dGpu / 12GB Ram / 256GB SSD
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eGpu Hardware:
Razer Core X + RX 580 (Sapphire) + Apple TB3 to TB2 Adapter + Apple Official 1M Thunderbolt 2 Cable
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Installation Steps:
1. Assemble eGpu.
2. Time Machine backup on nMp.
3. Eject/unplug all drives and unnecessary devices from nMp.
4. Meet PreRequisites from the Purge Wrangler Script. Including disabling System Integrity with restart in Recovery.
4A - I made sure I logged in to Terminal using the Recover Mode (Restart System - CMD+Option+R -- at startup)
4B - Run Terminal - type - csrutil disable
4C - Turn off Secure Boot - Utilities > Startup Security Utility
4D - Restart System
5. Ensure System Integrity is Disabled.
6. Install purge-wrangler Script.
7. Follow Option for AMD cards.
8. Do not enable Ti82.
9. Restart.
10. Connect eGpu to nMp via TB2 Adapter. And ensure it is recognized.
11. Changed options on apps (right click, Get Info - or CMD-i) to prefer external GPU.
Late 2013 Mac Pro - Quad Core 3.7 / Radeon Fire Pro D300 dGpu / 12GB Ram / 256GB SSD
2013 Mac Pro (FP D300) [3rd,4C,E] + RX 580 @ 16Gbps-TB2>TB3 (Razer Core X) + macOS 10.14.1 [build link]
@victored In order to have the eGPU connected at boot, use either Thunderbolt Port #5 or #6. They are the bottom two ports. We found it's more eGPU friendly and don't cause the boot process to hang.
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2021 Gigabyte Z590i Vision D [11th,6C] + RTX 3060 Ti @ 32Gbps-TB4 (Gigabyte Gaming Box) + Win11 [build link]
Oh - im going to try that. I am at port 3 (the middle left) right now. I will report and edit the post if it works.
OMG @itsage ... this is amazing! It worked. Y'all are geniuses 
Late 2013 Mac Pro - Quad Core 3.7 / Radeon Fire Pro D300 dGpu / 12GB Ram / 256GB SSD
2013 Mac Pro (FP D300) [3rd,4C,E] + RX 580 @ 16Gbps-TB2>TB3 (Razer Core X) + macOS 10.14.1 [build link]
Thanks for the post. Am considering trying this egpu set-up, did you use the Pulse or Nitro+ card? Cheers
To do: Create my signature with system and expected eGPU configuration information to give context to my posts. I have no builds.
.@timbousm - i have the Pulse. I actually had the Sapphire Pulse Vega 56 first but I noticed that it didn’t boost my multi-cam editing on my 2016 Macbook Pro 15” with RX 455. So I tried to go down and save money and got the Pulse RX 580. I am actually happy to save $130 and get very close to the same performance.
Installing the eGPU to the Mac Pro Late 2013 was just a bonus for Fortnite. LoL
Late 2013 Mac Pro - Quad Core 3.7 / Radeon Fire Pro D300 dGpu / 12GB Ram / 256GB SSD
2013 Mac Pro (FP D300) [3rd,4C,E] + RX 580 @ 16Gbps-TB2>TB3 (Razer Core X) + macOS 10.14.1 [build link]
@victored do you think this set-up would assist in FCPX? In built graphics card is seriously straining 🤯
To do: Create my signature with system and expected eGPU configuration information to give context to my posts. I have no builds.
.It does help with FCPX.
Late 2013 Mac Pro - Quad Core 3.7 / Radeon Fire Pro D300 dGpu / 12GB Ram / 256GB SSD
2013 Mac Pro (FP D300) [3rd,4C,E] + RX 580 @ 16Gbps-TB2>TB3 (Razer Core X) + macOS 10.14.1 [build link]
Is there any way to attach Thunderbolt monitors to this? I have two of them to drive.
Mac Pro (Late 2013) 2.7 GHz 12-Core Intel Xeon E5 | 32GB | AMD FirePro D700 6144 MB | Dual 27" Apple Thunderbolt Displays | 1TB SSD | 10.12.6
What kind of Thunderbolt monitors?
A Thunderbolt monitor needs to be connected to a Thunderbolt port. Connect them to the Thunderbolt ports of the Mac Pro. If the Thunderbolt displays are 5K then you'll need to use a Thunderbolt 3 add-in card like the GC-ALPINE RIDGE or GC-TITAN RIDGE for each Thunderbolt display. You won't be able to use the non-display features of the display (USB, Audio, Camera, etc.).
I just have two 27" Apple Thunderbolt Displays of the non-4K variety. Will this (or any) eGPU setup provide a benefit to me if I can't connect the displays directly to the eGPU?
Mac Pro (Late 2013) 2.7 GHz 12-Core Intel Xeon E5 | 32GB | AMD FirePro D700 6144 MB | Dual 27" Apple Thunderbolt Displays | 1TB SSD | 10.12.6