Sometimes, it's not a static mesh that the issue. You can have a perfect mesh when the truck is standing still, but if the motor mount flexes with jumps or whatever, the mesh will be affected. A solid, consistent is VERY important to the life of any spur. What kind of motor mount setup do you have?
Another thing to consider is that most spurgears have got an off-centre hole in them. The paper trick works in an ideal world, but with an off-centre hole the paper needs to be on the place where the gears are as close as possible.