From your reply it looks to me as though bottom of the strut housing (where the wiper seal fits) has been impacting the spindle, at least that's what the photo seems to indicate. If I had to bet I'd have said the strut had too little oil in it rather than too much. The oil quantity controls the damping rate, the nitrogen gas pressure the initial ride height either loaded or empty. Reduced Damping will permit the strut to both bottom and top out on anything less than a billiard table, especially loaded.
Another question. Does it have a payload system installed and do you use the numbers..? If so is this truck averaging maybe 5-10% less payload than the other trucks in your fleet..? I'm assuming you have more than one truck.
Our road conditions are pretty average so I am leaning toward a Wheelie situation or too fast over big bumps in the terrain.
You don't have average roads if your trucks can wheelie, more like poor or very poor by the standards I'm used to.
