Modifying the suspension ride height is a very bad idea. A lot of research and development went into designing the geometry so the steering, braking, and suspension all work together. Besides the resulting tire wear you will have and the miserable ride quality, lawyers and insurance investigators love to find stuff like that. Even if the other guy ran the red light and hit you, a good lawyer will convince the jury you were partly at fault for the crash because you were less able to avoid it.
An alignment can be performed that will bring the wheels back to specs while the truck is sitting on the hoist, but the change in geometry will cause terrible tire wear as the truck goes up and down over bumps in the road. "Steering axis inclination, (SAI) will be changed which affects braking and handling, especially when just one tire hits a bump in the road.
Every alignment shop has a book with published ride height specs for every vehicle and where to take those measurements. Few vehicles even allow up to one inch of spring sag before they must be replaced. Ride height is that critical.