Stutter:
Sounds like something might be off with the Link connection. vorpX can be quite demanding, but with your PC most games should work well. If you are sure that Link itself works fine, try to lower some ingame graphics settings. Depending on the method converting a game to stereo 3D costs ~10% (Z3D) to ~50% (G3D) performance. On top of that there is some additional overhead caused by sending the game to the headset.
So even with a 5090 in demanding games you may have to lower some settings to account for the stereo 3d performance impact and to ensure that there is some headroom left for smoothly sending everything to the headset.
Resolution:
You have to set the resolution in the game options or in the vorpX menu for game profiles where vorpX can handle that automatically (vorpX shows a notification on start if that’s the case for your game). To get higher resolutions than your monitor allows, please check the ‘Custom Resolutions’ section in the vorpX help. For ‘FullVR’ mode you typically want a 4:3 res, for cinema/immersive screen 16:10 or 16:9 work best.
General:
To familiarize yourself with how vorpX works you should definitely check the various guides in the vorpX help. At the very least the ‘Essential Hints’ section. That’s time well spent, will answer a lot of questions you may have.