NEWPORT BEACH, CA – Toyota Motor Sales U.S.A. Inc.’s Lexus brand will launch a next-generation GX SUV this fall, a source familiar with the plan tells Ward’s.

The GX, a midsize body-on-frame SUV that shares a platform with the Toyota Land Cruiser, debuted in the U.S. in 2003 as an ’03 model.

The upcoming model will get Toyota’s new 4.6L V-8 engine, the source says. The small V-8, which debuted in the ’10 Toyota Tundra, making 310 hp, will replace a 263-hp 4.7L V-8 in the ’09 GX.

The next GX also will receive a new interior design as well as updated interior features such as a next-generation navigation system. Additionally, it will sport revised sheetmetal and body panels including a different rear door, the source says.

Lexus General Manager Mark Templin declines to confirm the new GX but says the brand wants a continued presence in the segment.

“The largest SUVs have been hit the hardest, but there’s still a segment of the population that wants those vehicles,” he tells Ward’s here during a media preview for the Lexus HS 250h sedan.

“(SUV owners) tow things. They play hard. They do a little bit of off-roading, not much. More than actually doing it, they want to know they can do it if they have to. We still think there’s a viable market with our GX.”

Lexus hoped to sell 20,000 GX units in the SUV’s first full year of sale when it debuted in 2003 as a stopgap between the midsize RX cross/utility vehicle and large LX SUV. However, sales in recent years have underperformed that figure. Deliveries in April plummeted 66.1% from like-2008 to 2,210 units.

The GX’s best sales year was 2004, when it sold 35,420 units.

Ward’s data shows the GX’s segmentation group, Luxury Middle SUV, posted the fifth-largest decline of all U.S. light-vehicle segments in the first four months of 2009, losing 52.8% of its volume through April compared with year-ago.