Vehicle issues

So I parked my vehicle and did some stuff, cleared some areas so it would fit, standard things, really. I come back and get in, and what do I see?

It happens when I step into the driver’s seat. Once I press space, I can step out, walk around the car, get back in, and it doesn’t repeat.
I can start the car, fiddle with my installed things, and sit and wait as much as I want. As soon as I give it gas, however, it glitches out hard.
It, like, throws me out of the cabin? And I teleport around a bit after it throws a Vehicle Not Found error. The car coasts to a stop, or doesn’t, it varies.
If I don’t press any movement keys, just wait, I scoot along the ground, even over mines, and when I can see it, so does the vehicle.
If I throw it into reverse, after I regain control after the teleporting, I still can’t trigger mines, and I can only walk so far south until I teleport back north to my starting point. I can walk all other cardinal directions just fine.

I searched for this and found similar problems, and I uninstalled/re-installed the seat, no dice. What do I do? I gotta get this convoy to the next town, man.