Before attaching the pitman arm, I attached the steering wheel and it did have equal turns to either side from center at that point. After attaching the pitman arm though, the problem was there again.
Sounds like you did have the steering box centered. Question,... Assuming the steering gear was centered, and the wheels were straight, did the pitman arm line up with the center link. If so, it sounds like you have everything installed correctly, and I would follow the suggestion 340Duster gave you. Check to see what your travel stop is, and what is limiting your travel.
Another thing you could do is disconnect the pitman arm and check the travel distance of the tires in each direction to see if they move further in one direction than the other. This would eliminate the steering box from the equation and let you see the range of steering the tires have. Then, like 340Duster said,... See what is limiting the travel.