Here's what I'd do:
Jack up the truck & support on jack stands so each front tire is only about 1" off the ground. Then put a strip of duct tape around the center of each tire, or wide masking tape. Then spin each tire, and hold a sharpie against the duct tape to draw a thin line all the way around.. brace the sharpie agaist a 2x4 or something so it doesn't move sideways, but do allow it to move in and out a little to compensate for any out of roundness of your tire.
then measure the distance between the lines in front, distance in back, and compare. I think the ideal setup is right around 1/4" less in front than in back, perhaps an expert could chime in to correct me if I'm wrong. The adjustment is made on the drag link, which is the bar that connects the two wheels together. Not the tie rod that connects the PS tire to the steering arm, that's where you adjust how centered your steering wheel is.
That's the simple version, I'm sure it can be more complex than that.. hth!!
82 fj40, 99 uzj100, 06 gx470
97 DR650, 05 525EXC, 06 TW200, 89 TW200, 09 TTR125, 07 TTR90, 07 CRF50