AI and Friend is slower than me?

When playing with friends, on a WAN, I notice that every time I'm near my friends, every car seems to be stuttering/lagging or something. A lot of times we crash into each other because of sudden jumping in front of each other. Anyways, I've also noticed that at least one of my friends seems to be a lot slower than me with the exact same car and everything. It also seems to affect other cars in the area. AI Cops and Racers will be a lot slower, I can keep up by tapping on the accelerate button, instead of having to actually drive. When they AI leave the affected area, their speed matches mine again. Any idea what's going on? Could it be that the other computer can barely run it? It is on medium graphics, (switching it to low on everything appears to make the game have random pauses that last almost a second and they're frequent.) but it is pretty laggy.