It sounds like you’ve taken the right initial steps with DDU and driver installation. However, if you're still facing severe lag, here are a few quick checks that might help:
1. **Power Settings**: Make sure the power settings in your AMD software are set to performance mode, not balanced or power saving.
2. **Check GPU Temps**: High temps can cause the GPU to throttle, so monitor temps during use with software like MSI Afterburner.
3. **BIOS Update**: Sometimes, an outdated motherboard BIOS can limit new hardware performance. Check for any updates.
4. **Reinstall AMD Software**: If the driver installation had any issues, a fresh reinstall might help.
5. **PSU Check**: Ensure your power supply is delivering enough power, as AMD GPUs can be power-hungry.