Set up custom pathfinding for the truck objects, and give them both the Add Pathfinding Obstacle Truck and the Avoid Moving Over Truck. Then regenerate each one's obstacle map periodically, since they're moving objects. I think that should solve a majority of your issue.
Alternately, have an invisible Sprite (use bounding box collision) with a larger radius than each truck follow them around (and probably match their angle), and use that for their pathfinding instead of the trucks themselves. It would give you a little less of that "trucks crashing into each other" effect. This gets trickier, though, since you'll need to account for each truck's own invisible sprite so that it will actually move at all.
Beyond that, there's something to be said for checking if the trucks are within a certain radius of each other, then if so, using the LinearAim System expression to find out where they're headed and then veering away from that point. It's going to take a little more number-crunching and finessing for you to do to get it the way you like it, but it might be the most satisfactory option when you're done.