R9 380 no output after booting?

[iamMacPerson]

I have a 4,1 to 5,1 conversion that used to have a GTX 970 in it. I got tired with the driver issues, and it's mainly used as backup machine, so I sold the card and switched to an R9 380 since they have native support. Whenever I boot the machine, the monitor seems to get some signal from the card, but no video as it just triggers a 'Monitor Sleep' notification. Logging into the machine over Screen Sharing shows that it's outputting at a low, square resolution video without acceleration. If I unplug the cable from the card and plug it in, it'll come back fine at it's scaled 2560x1440 resolution without issue.

I'm using a Dell P2715Q 4K monitor over a Mini-DisplayPort to DisplayPort cable. Mac Pro is running macOS 10.13.5 and the card is in PCI slot 2 (because I didn't realize it had a back plate when I bought it).

EDIT: Interesting update. I did an SMC and PRAM reset, and the machine seemed to be taking longer than expected to boot. Turns out it Kernel Panicked. The most interesting part is two lines near the beginning: "BSD process name corresponding to current thread: DumpGPURestart" and "last loaded kext at 7823490837: com.apple.driver.AppleUpstreamUserClient 3.6.5 (addr 0xffffff7f9abbe000, size 36864)". Ideas?

 

[h9826790]

I have a 4,1 to 5,1 conversion that used to have a GTX 970 in it. I got tired with the driver issues, and it's mainly used as backup machine, so I sold the card and switched to an R9 380 since they have native support. Whenever I boot the machine, the monitor seems to get some signal from the card, but no video as it just triggers a 'Monitor Sleep' notification. Logging into the machine over Screen Sharing shows that it's outputting at a low, square resolution video without acceleration. If I unplug the cable from the card and plug it in, it'll come back fine at it's scaled 2560x1440 resolution without issue.

I'm using a Dell P2715Q 4K monitor over a Mini-DisplayPort to DisplayPort cable. Mac Pro is running macOS 10.13.5 and the card is in PCI slot 2 (because I didn't realize it had a back plate when I bought it).

EDIT: Interesting update. I did an SMC and PRAM reset, and the machine seemed to be taking longer than expected to boot. Turns out it Kernel Panicked. The most interesting part is two lines near the beginning: "BSD process name corresponding to current thread: DumpGPURestart" and "last loaded kext at 7823490837: com.apple.driver.AppleUpstreamUserClient 3.6.5 (addr 0xffffff7f9abbe000, size 36864)". Ideas?

Completely power down the monitor. Remove the power plug for 10 seconds. Then power it back ON.

If still nil help, try different DP settings (on the monitor side), e.g. switch from DP 1.1 to DP 1.2 etc.

 

[iamMacPerson]

Completely power down the monitor. Remove the power plug for 10 seconds. Then power it back ON.

If still nil help, try different DP settings (on the monitor side), e.g. switch from DP 1.1 to DP 1.2 etc.

Will do. I'll try that when I get home. I have no problems with my MacBook Pro using the same monitor using a DisplayPort to Mini-DisplayPort cable.