During our day-long testdrive, we hitched up an F-250 Super Duty to a loaded twin-axle trailer (combined weight: 10,000 pounds) for a leisurely towing exercise through some twisty two-lanes around the Bradshaw Mountains of Arizona. The Super Duty didn't seem to notice the extra weight at all, and its slightly-overboosted-with-no-load steering delivered a pleasantly on-center feel in corners under the modest load. A bit later in the day, the Ford engineering folks gave us the chance to hook up to an 85,000-pound wheel loader at a nearby gravel quarry to test the Super Duty beyond its intended limits. Lamely attempting a hole-shot throttle-punch maneuver, we didn't get very far before our tester's rearend and springs began chattering, then barking, in protest. Take it slow and steady off idle, though, and you can literally move mountains with this truck.