Toyota Motor Sales USA Inc. reveals details today of its fifth-generation Toyota 4Runner SUV, a redesigned vehicle that sticks with its body-on-frame skeleton but comes to market with a more fuel-efficient powertrain.

TMSUSA calls the ’10 4Runner “more rugged and athletic, and packed with more power and better mileage.” It is taller, wider and longer for ’10, sharing the same platform as the smaller FJ Cruiser but adds extensive frame and body reinforcements.

Under the hood, the 4Runner receives a new 4.0L V-6 engine producing 270 hp and 278 lb.-ft. (377 Nm) of torque. That’s 34 more hp than the previous V-6 and 10 additional ponies over the previous V-8 engine.

Combined with slipperier aerodynamics, the new 4Runner’s fuel-efficiency improves from 16-21 mpg (15-11 L/100 km) city/highway to a rating of 17-23 mpg (14-10 L/100 km) on 2-wheel-drive models, and from 16-20 mpg (15-12 L/100 km) to 17-22 mpg (14-11 L/100 km) with 4-wheel-drive models.

Both models achieve a combined-cycle, Environmental Protection Agency-rated 19 mpg (12 L/100 km), an improvement of 19% over the previous generation, but still boast a maximum towing capacity of 5,000 lbs. (2,268 kg).

TMSUSA also will make the 4Runner available with a carryover 2.7L 4-cyl. engine, rated at 157 hp and 178 lb.-ft. (241 Nm) of torque and achieving fuel economy of 18-23 mpg (13-10 L/100 km) city/highway.

Toyota designers also tinkered with the exterior and interior of the 4Runner, which first debuted in 1984 and has sold 1.5 million units since. TMSUSA says the new design includes “rugged new bumpers and wider shoulders,” as well as newly styled headlamps and taillamps.

Among the improvements inside, the 4Runner’s front seats gain a greater range of movement fore and aft; the instrument housing is brighter, more visible and now includes fuel-efficiency feedback; third-row seating is expanded; and a new cargo system takes advantage of a fold-flat second row.

A new “party-mode” setting is added to available audio systems, which raises the bass and transfers the equalization to the rear of the vehicle for tailgating.

TMSUSA will make the 4Runner available in three trim levels – a Trail edition that emphasizes off-road capability and Limited and SR5 grades that include premium features.

“In 1984, the first 4Runner helped cultivate and foster the up-and-coming SUV market,” says Bob Carter, group vice president and general manager-Toyota Div. “When the new 4Runner launches later this fall, it will continue to be a perfect fit for young, and young-at-heart, outdoor and off-road enthusiast.”

Pricing on the new 4Runner has not been released, although ’09 models start at $28,640 for 2WD and $39,360 for top-of-the-range 4WD variants.