Two-mode adds about $3500 to the price of a Sierra pickup and is offered only with a crew cab and a 6-foot bed (which has an actual floor length of 69.3 inches.) Why just a crew cab? Because the battery pack is bulky and requires fastidious temperature control so it can't readily be stashed under the bed floor. Also, it would consume too much interior space inside regular and extended cabs. While the cushion portion of the rear seat hinges up, the space available for cargo in the back of the crew cab is diminished by the battery pack.
Chevrolet offers the same basic package on Silverado crew cab pickups which begs the question, what's the real difference between a Sierra and a Silverado? Mechanically, they are identical. Interior decor is also common. The distinction is all in exterior design. Each of these twins has its own front fenders, hood, grille, and front fascia. The shape of the rear fender surfaces is also unique to each brand. For the privilege of shopping at a GMC dealer versus a Chevy showroom, you will spend an extra $370.
Two trim levels are available. The base 2wd Sierra two-mode costs $39,365 including destination. Adding 4wd boosts the sticker by $3150. (StabiliTrak electronic stability control and a locking rear differential are standard on all Sierras.) The $6135 premium trim package adds leather trim, power front bucket seat adjusters, a center console, a Bose sound system with navigation, a hard bed cover, and several minor convenience items. The only optional equipment is a $995 moonroof with premium trim and power seat adjusters with base trim.
To study real world towing capabilities, I hauled a 23-foot SeaRay boat on a tandem-axle trailer on a 200-mile journey down Interstate 35 south of San Antonio, Texas. That payload weighed 5400 pounds, well within the 5900 pound tow rating GM assigned to a 4wd Sierra (lighter 2wd editions are rated for 6100 pounds). Hustling the rig to 60 mph from rest required only 18 seconds of smooth acceleration. A 30-60-mph passing maneuver took 13.6 seconds versus 7.3 seconds without the trailer attached.
While cruising on level ground, the engine stayed in 8-cylinder mode and there was no hint of strain holding 70-mph on grades. On downgrades, the driver information display reported an occasional shift to the V-4 running mode. There was no extra vibration or change in exhaust note during or after that transition.