My 5090 FE Keeps Crashing in My New Build—What Should I Do?

Hey everyone, I just built my first PC and everything seems to be running smoothly apart from my 5090 FE graphics card from Best Buy, which keeps crashing. The system randomly reboots with a 0x116 error (TDR error) in Event Viewer after the crash. Here's my setup for reference:

- ASUS ROG STRIX X870E-E GAMING WIFI
- AMD Ryzen 9 9950X3D
- Corsair Vengeance 6000 2x48GB
- Corsair TITAN 360 RX LED
- Super Flower Leadex III ATX 3.1 1300W
- Samsung 990 PRO 4TB
- Xiaomi 34-inch Ultrawide Curved Monitor
- Corsair 3500X case with multiple fans, so temp shouldn't be an issue.

I've tried a lot of troubleshooting steps already:

- Using DDU to reinstall various drivers, including the latest ones.
- Reinstalling Windows.
- Updating the motherboard BIOS.
- Clearing CMOS.
- Switching power supplies to a Corsair RM1200x.
- Trying different RAM.
- Reseating the GPU and power cable.
- Adjusting PCI-E settings.
- Turning off hardware accelerated switching in Windows.
- Adjusting various BIOS settings.
- Using a 1000W sine wave UPS for clean power.
- Testing with different cables and refresh rates.
- I've even RMA'd the GPU twice.

The crashes are random—happening while watching videos, but I can run stress tests like Furmark without issues. It's puzzling because my GIGABYTE RTX 5060 works perfectly, and integrated graphics is fine too. I'm starting to feel hopeless; what are the chances I ended up with two faulty GPUs in a row? I've replaced almost everything in my system except the CPU and motherboard.