Gas-only and Hybrid Sierra trucks share some common ground in room and cargo space.
In either, there's plenty of space and wide, flat seats across the front. Sierras come as five-seaters or as six-seaters, depending on cab configuration and whether a front bench seat is specified. The bench's dash is a workmanlike piece that sits high, leaving a middle passenger some decent legroom. With the bucket seats comes a center console with an agreeably styled dash, big gauges, and big controls that still can be operated when wearing gloves. "You sink into the cushy seats," according to Cars.com, and while Edmunds reports that the "seats are comfortable for long drives," other reviewers find the wide, flat seats to be unsupportive. ConsumerGuide reports "ample room for adults" up front, although "both the bucket and bench seats lack side support in fast turns but are firm and comfortable" otherwise.
Buyers can choose a regular cab with almost no room behind the front seats; an Extended Cab with space for tools and gear; or a Crew Cab for three-across adult seating. The stadium-style rear seat on Crew Cabs has a 60/40-split design and can be folded up for more cargo space, but it sits more vertically than in other full-size trucks. Despite its size, the Sierra's backseat suffers. Cars.com "was expecting it to be a little more spacious and comfortable," and observes the reviewer's legs "were touching the back of the front seat." Worse, "the rather upright backrest isn't very comfortable." ConsumerGuide also notes "legroom is ample in the crew cab" up front, but it's in "short supply" in the back.
There's some extra space inside the Sierra, depending on the model. For extra versatility, either section of the split seat can be stowed independently, allowing room for both cargo and a rear-seat passenger, and the rear access doors on extended-cab models open 170 degrees. ConsumerGuide reports that, "in front, the bucket seats come with a roomy console bin, while the bench seat is available with a flip-down center armrest that doubles as a large storage bin." MotherProof also notes that "cupholders are everywhere, and the center console is large enough to house a good-sized purse [or] CDs." Hybrid Sierras come only in the Crew Cab body style, though, and the space under the rear seat is occupied by the battery pack. Unfortunately, there "are few other interior storage cubbies"; Edmunds complains about "mediocre interior storage and cup holders."
The Sierra 1500 / Hybrid range has three bed lengths, depending on the model. Crew Cabs and Hybrids have a 5'8" bed; all versions except the Hybrid can have a 6'6" bed; and all versions except the Hybrid can be fitted with a long 8' bed. Automobile mentions the standard six-foot bed "has an actual floor length of 69.3 inches."
Materials are better than the truck norm, and fit and finish are above average in the Sierra. ConsumerGuide attests that "gauges are easy to see and read," and "interior materials are better than expected of a work-oriented truck." The Car and Driver reviewer comments that it "surprises us just how pleasant the interiors of GM's full-size pickups have become." MotherProof is "surprised by the level of comfort in the interior," which contrasts sharply with the "no-frills finishes" of the pickups of the 1980s and '90s. Edmunds praises the interior's "tight build quality," and ConsumerGuide reports that "road noise in Sierra is lower than in most pickups...wind noise intrudes only above 60 mph." Automobile says that the GMC Sierra Hybrid's powertrain is "notably quieter overall than any conventional powertrain," while ConsumerGuide observes that "wind noise intrudes only above 60 mph."