Jack the front of the truck up, and using something that will hold stationary, spin each tire, and scribe a line around the circumference of the tire, in the middle of the tread. this can be tough, so be patient.
Then, you can do the measurement lifted, or on the ground. I usually do them on the ground, simply take the measurement at the front of the tire at the highest point you can stretch the tape across. Then, do the same at the rear of the tire.
Make the distance on the front of the tires, 1/32 - 1/16 inch LESS than the distance on the rear of the tires. Tighten things down, and go for a test drive. If it hunts or darts, you are still toed out too far, and need to bring the front in a little more.