Be advised. I am ASE certified in suspension and brakes. Something is going out / or something is loose. I last actually aligned the dually about 4 years ago. I have touched it up from time to time, but it hasn't officially required any adjustment. I check it yearly, but I have my own alignment rack. If you actually need an alignment, something has been bent, moved, or worn out.
Someone hit a curb and not tell you?
Hell go out to Desert Bar once, that will square it up for you.