I've started to play some GTA SA from a new campaign and I have some issues. I'm using the SA FPS limiter to set it to around 30 fps.
During the mission when you are on the bike escaping the Russians and the one where you throw crates from the train, the vehicles driven by NPCs are really glitchy. It looks like they are lagging or jittering or something. Especially when Ryder is driving his car when you throw the crates, his car is like shaking or something. Look at 3:22 on this video to see what I mean.