You're onto the right answer. At some point:

1. the middle of the lory would be the center of gravity of the lory, and no longer have any grip on the road. Making it a space lory with the lower parts dragging in the atmosphere.
2. the top of the lory would be so tall that if it was driving, the change in angle of a fraction of a degree would make the top of the lory travel faster than light to keep up. This might happen sooner than running into other stars. If the lorry is 1 light year tall and goes over bump that changes its angle by only 1 degree, the top of the lory would move 1.6 x 10¹¹km within a few seconds. So the lory might sheer apart, or would sway like a skyscraper in wind with each molecule moving at the speed of light all over the place as the truck bumps around on a road where even minute variations would make the top move wildly.