The production H3T will come with the same tiedown system and bedliner style as found in the new full-size GM pickups, and for those who like to carry ATVs and other loads, the bed measures 48 inches between the wheelwells. It also has top-access bedrail cargo bins on each side for added storage and a bed extender to accommodate longer cargo needs. The trucks we're driving are equipped with the Adventure option package, which includes 33-inch Bridgestone Dueler A/Ts and an electric-locking front differential-both of which are invaluable on this trail.

As Daryl Ehrlich, H3/H3T powertrain development engineer, muscles a race-style Craftsman floorjack between the broken-down mule and the boulders underneath, John Chapman, the head wrench who is also a technician at GM's Desert Proving Grounds in Arizona, pulls out an electric impact wrench.

I look at my watch. Less than 20 minutes have gone by since the CV joint disintegrated. The tire's already back on the hub, Chapman is wiping axle grease from his hands, and we're ready to get moving again.

Dominic Rimmer, the H3T vehicle performance integration manager, climbs into the seat next to me. He's come from Brazil, where he usually splits his time between production and engineering for the H3Ts built for markets outside of North America. (H3s for foreign markets are built in South Africa; foreign-market H3Ts will be built alongside the Colorado/Canyon in Brazil.) As we slowly make our way along the remaining mile of trail, he explains the basic evolution of the H3T.

In the first phase, the idea is brought to life virtually-using powerful computer-aided drawing programs-and physically as a one-off, "Proof of Concept" vehicle handbuilt by the team in GM's Experimental Engineering facility at Milford Proving Grounds. The resulting 134-inch-wheelbase concept pickup looked good despite welded-on door extensions and mix-and-match parts from other vehicles.

But sophisticated computer simulations and early development drives of the hand-built Proof of Concept truck revealed the longer-wheelbase H3T needed a number of upgrades and changes.

Rimmer says after those initial changes were made and the team had a definite direction for the truck, they handbuilt two-dozen mules in Warren, Michigan, to use as rolling design and engineering test platforms. These mules are put through a seemingly unending series of tests at GM proving grounds around the country, in real-world driving conditions, and in extreme environments from Death Valley to the Swamp Lake Trail.

Such a development process is what brought about the reinforced drop-frame on the new H3T; larger-diameter front and rear anti-roll bars; recalibrated shock tuning; V-8 steering pump on the five-cylinder model; a quick-steering rack and pinion for I-5 and V-8 models; higher-capacity cooling system; and standard 32-inch tires on new 16-inch steel wheels, plus the option of 33s and an electric locker.