Honestly, in very dry, loose conditions as you described, tires are probably not the biggest issue. No tire is going to magically give you grip when there is no grip to be had. Depending on wear, you want to run the softest tire you can get away with. Thread pattern that would probably best would be a Cityblock, caliper or digit type thread.
But the biggest thing, is slow down. Slow is fast, buzzing the tires and sliding into and out of the corners is nothing but a waste of time and equipment. Keep the truck straight and square on the track and drive smooth on the throttle and braking, I guarentee that will be faster and more consistent.
Outside of driving and tires. drop your center diff fluid 2-3K maybe more depending on what you have now. soften up the clutch springs and possible even consider carbon shoes instead of Alum.