Most mdt's and hdt's have a pretty good turning radius to start with, I know my Topkick turns on a dime as compared to my extended cab dually. I can make a U-turn in that where the dually would have to back up twice, and the wheel base is 6' longer than the dually. Obviously the wheelbase affects that on your truck, but there are rigs way longer than yours out there pulling really long race trailers.
I would check for steering bump stops, normally located on the axle, which limit the travel of the spindle and how sharp you can turn. Normally those can be shortened or modified to allow the truck to turn sharper. You do have to be careful that you don't let it turn sharp enough where you can damage anything like steering components, suspension components, air lines, etc.. Basically first you need to find the stops, normally one on each side, and with the steering wheel as far as it will go in either direction determine if there is enough clearance to allow the wheels to turn sharper. Make sure the tire will not rub on anything critical, and the steering will not bind. At that point you can shorten the stops to allow more steering travel. Be conservative at first, easy to trim a little more, harder to put it back if you find you cut too much.