Been having the same issue with gsx vehicles stuttering ever since I built my new pc in late October. I was first running on DX11 but later switched to DX12 with Frame generation on, which made no difference. I've been trying to solve the issue since it started but can't figure it out. It wasn't happening on my old pc. Whether 2.8.2 is the isssue I'm not sure because my last flight on my old pc was a few days after 2.8.2 had released. I can't remember for sure whether I had updated to 2.8.2, but I usually check gsx for updates via fsdt installer almost every day so there is a high possibility that I was running 2.8.2 without any issues. The stuttering happens with every aircraft I have tested so far: PMDG 737, Fenix A320 and FBW A320Neo. It happens at both default and addon scenery. I do recall the stuttering smoothening out or almost dissapearing completely when at heavy scenery where fps is closer to 30fps than the usual 40-60fps I get. If I'm correct this seems to point to SimConnect not being able to keep up or something like that. The next question is how can it be fixed then? I've seen plenty of people with similar or the same pc specs as mine running MSFS with GSX at the same fps with no problems. I also tried closing and uninstalling 3rd party software that uses SimConnect and also unplugging any peripherals that I felt might have been contributing. No difference. I have updated both the chipset drivers and the Nvidia drivers to no avail. The Nvidia drivers have had 2 or 3 updates since building my pc, none of them have made any difference. I don't really know how to check whether a windows uppdate is the problem or not.
My specs:
Ryzen 7 7800x3d
Nvidia RTX 4090 (MSI suprim x)
32GB G.Skill trident z5 neo rgb (EXPO not enabled, have tried enabled)
1TB Samsung nvme for Windows and a few other programs (gsx also on this drive)
2TB samsung nvme for flightsim and games
Logitech Extreme 3D Pro
Honeycomb Alpha and Bravo
Saitek rudder pedals
Asus MG278 2560x1440p @144hz