Both should wear on the inside, but I have see just one like yours is doing. Its easy enough to check toe end.
First, scribe a line around the center of the tire using a sharp pick.
Next roll the truck forward on a level surface so the tires make at least one to two full revolutions, let it come to a stop with out using the brakes.
Third, measure the rear of the tires as high up on the tread as you can with out hitting the bottom anything like exhaust or transmission.
Forth, move to the front and measure from the same hight. Subtract the front from the rear and you should have you toe end. You are looking for 1/16" to 1/8" toe-in.
If the steering is worn out you need to fix it before working on the tierod adjustment.
Joe
