iMac 2019 GPU Problems

Ugh, the system crashed while posting this, and I couldn't finish editing it in the 'edit' window. Can't seem to delete posts either. Here is my revised post:

Recently bought a 2019 21.5” 4K iMac with i5 8500, 8GB 2666MHz RAM, 1TB Fusion (1TB HDD + 32GB PCIe SSD), RX 560 4GB. It was New Open Box from eBay, and from what I can tell has never been used. 

I have upgraded all of the internal components to i7 8700 (used), 32GB 2666MHz RAM (Some OEM Micron, used), 1TB NVMe (SX 8200 Pro with Sintech Adapter), 500GB SATA SSD (Crucial, not in use), and GPU obviously unchanged. High quality thermal paste (Thermal Grizzly Kryonaut) was used on the GPU and CPU. 

The macOS was updated to 10.15.3, Trim has been enabled, and Migration Assistant used for our data on a Mid 2010 iMac running 10.13.6.

So, now the problem. After the restore and initial usage, the machine was fast, but not as snappy as it should be for the hardware installed. I attributed this to all the indexing going on and the backup taking place. But after an nVRAM and SMC Reset, the computer really picked up speed and didn’t fall back.

The GPU is acting up and I don’t know why. The first problem noticed was that using iStat Monitors showed that while the GPU processor usage was extremely low VRAM usage was often completely maxed out (All 4GB). This is without doing any visual tasks. Upon investigation it appears the Curating Process in Photos and maybe the Time Machine backing up could be causing this. Now it seems mostly stable (under 50%) but occasionally it will ramp back up.

Then we began seeing artifacts on the screen, mostly elongated diagonal triangles and lines. These could easily be removed by just dragging a window over the affected area, kind of like erasing them on a drawing board. These are not very common.

Next came the shutdowns…at some point when asleep it seems to shutdown. One time when I clicked Report after the problem was shown I read Panic Caller 2 before the window was closed for some reason. Upon looking at the Shutdown log, all reasons for shutting down (a total of 9 in the last 24 hours) have been code 3 IE a Hard Shutdown. I know for a fact that I have only done this ONCE. Looking at the console shows a lot of sleep wake failures, like it broke the limit in Google Chrome and iStat for how many times it tried to wakeup. Then there were several crash logs, all Adobe except for a Windows Server one.

Now today Photoshop CC 2018 is saying “Photoshop has encountered a problem with the display driver, and has temporarily disabled enhancements which use the graphics hardware”

I haven’t even looked into the specifics of Adobe’s suggestions, because I know it’s not Adobe specific.

It is under the stock AppleCare warranty still until June, and I have read that upgrading parts doesn’t void warranty, but if you do and they know they will look for internal damage from you (but there isn’t so I think they will just try to blame me regardless before replacing the unit). Other forums recommend putting all the original parts back inside first, so they will only possibly see that the one internal warranty sticker is gone (and so they don’t keep my upgrade parts), of which I can mention open box.

The seller I purchased from also has a 90 day warranty, and they will not be cracking it open to see if I did anything.

So, what are your thoughts? Is the GPU defective? Or is it just running ragged due to something incompatible from the System Migration? Is my best bet to un upgrade and go to Apple or the Seller, or just test the machine running stock OS without the migration?