Well, you're only looking at an 80 HP deficit and 154 lb-ft torque advantage (on the diesel Titan). I'm willing to bet that during the whole rev range of the gas motor, and with gearing, it has more torque that it can effectively put down to the ground. On the Big 3 HD's, the worst case difference for diesel versus gas is RAM, which (considering only automatics), has a difference of 40HP between the HEMI 6.4 (410 HP) and 68RFE equipped Cummins RAM (375 HP). Then torque wise, the Cummins has about a 371 lb-ft advantage (800 lbft total). In Nissan's case, there isn't quite enough to differentiate their diesel from their gas motor capability wise. In the case for Chevy and Ford, the Diesels and Gassers either have nearly the same horsepower, or less horsepower than the diesels. Torque wise, well the diesels are both around 800 or 900 lbft while the gassers top out around 400 something. I feel Nissan should had aimed for something like a 350/650 power/torque rating. But the video does show that at its fully-loaded GCWR, the Titan adequately gets the job done with either powerplant. The gasser is just faster (and thirstier).
On the MPG front, results seemed to be what I expected. It basically ended as 3.7 mpg versus 3.0 mpg. May not sound like a lot, but that's either 19% or 23% better fuel economy for the diesel depending on which POV you take (Relative to gas or diesel?). I'm sure the case would be even better in steady-state flat ground towing since that's when the diesel is allowed to run even leaner and squeeze more fuel efficiency from partial state throttle.