What Actually Powers The New Lexus GX 550
The old GX 460 ran a 4.0-liter naturally aspirated V6 making 270 horsepower. Everyone complained about it. They were right. For 2024, Lexus dropped that engine and replaced it with a completely different powertrain that actually changes how the truck feels to drive. Under the hood sits a 3.4-liter twin-scroll turbocharged V6 code-named V34A-FTS. It makes 349 horsepower and 479 pound-feet of torque. That torque number is the one that matters most here. You get 85 percent of that torque available from just 1,600 RPM. The peak horsepower hits at 5,200 RPM. A 48-volt mild-hybrid system fills in torque fill under the turbos. This is called i-Force Max badging on the tailgate. The engine pairs with a 10-speed automatic transmission. Previously the GX used a 5-speed. That jump from five to ten gears is not cosmetic. It changes how the truck behaves on the highway and during passing maneuvers.
I spent about two weeks with a pre-production GX 550 at the Toyota test facility in Arizona. The first thing you notice is how quiet the cabin is at cruise. The 48-volt system cuts out the low-speed turbo lag enough that you barely register it. But there is one thing the brochures do not tell you about. At full throttle from a stop in fourth or fifth gear, the transmission will hold a gear longer than you expect. The turbo spools between shifts and the hybrid motor assists. If you floor it casually in overdrive, the truck actually moves slower than you might think because the computer is trying to stay in a tall gear. The workaround is simple: tap the selector to sport mode or manually downshift one gear before you press hard. It took me about twenty minutes to adjust my right foot to the new behavior. Once you do, it drives fine. The towing capacity sits at 8,500 pounds. The GTW is 9,100 pounds. That is a reduction from the GX 460 which could tow 8,300 pounds in some trims but the new truck carries more payload. The curb weight is roughly 5,300 pounds depending on trim. A heavier truck with more torque sounds like it should be slow. It is not. The 0 to 60 time lands somewhere around 6.7 seconds according to independent testing. That is a full two seconds quicker than the outgoing model.
The real-world fuel economy is the counter-intuitive part. Toyota claims 19 MPG combined. My testing got 20.3 MPG during mixed driving. At highway speeds holding 75 MPH it drops to about 22 MPG. The mild-hybrid helps during stop-and-go more than anyone expects. City driving is where you see the biggest efficiency gain from the 48-volt system. One thing beginners miss about this engine is the dual-scroll turbo layout. Each scroll feeds its own bank of exhaust pulses. This reduces cross-bank interference and keeps spool response sharper than a single-scroll setup at low RPM. The tradeoff is a slightly more complex exhaust routing. If you plan to run a cat-delete or aftermarket downpipe, you need to account for both banks having separate flow paths. A single-wide piping setup can cause check engine lights if the O2 sensor readings get imbalanced between the two banks. The AWD system is direct4 with a Torsen center differential. It sends torque front to back based on demand. At highway speeds it is predominantly rear-biased for efficiency. Off-road engagement drops the front output significantly. I tested this on loose desert washboard and the system felt predictable. There is a 4LO mode that adds a 2.646:1 reduction gear. That gives you crawling capability you did not have in the old GX.
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Braking performance is adequate but not outstanding. The 12.9-inch front rotors are ventilated. Rear rotors are 13.0 inches. You will find yourself braking a bit harder than expected the first few times simply because the truck feels lighter on its feet now. The extra torque makes you want to go faster. The same mass keeps you from stopping any quicker. If you are coming from the GX 460 the most jarring change is the steering feel. The electric power steering has been recalibrated. It feels more isolated from the road than the hydraulic system in the older truck. Some people like this. Some do not. It is a known discussion point in forums right now. There is no fix other than adjusting the steering sensitivity through the Drive Mode selector. Sport mode sharpens it by about 15 percent. Comfort mode softens it further. The engine oil capacity is 7.5 quarts with the filter. That is standard for this engine family. If you change it yourself use a synthetic 0W-20. The factory fill is meeting the API SP / ILSAC GF-6 specification. Do not substitute 5W-30 unless you are running extreme heat conditions like sustained towing above 8,000 pounds in temperatures over 95 degrees F. Even then stick to 0W-20 first and switch only if the temps are sustained.
A few owners have reported a rattling noise from the turbo plumbing during cold starts. It usually goes away after 30 to 60 seconds. This appears to be thermal contraction of the heat shields rather than a mechanical failure. If the rattle persists past two minutes of driving you should have it inspected. Several Toyota service bulletins cover heat shield bracket updates for this engine family. The transmission software is one area where Lexus has pushed updates over the air for early models. Some drivers noticed the 3-4 shift was hesitant during break-in. A firmware update addressed the shift timing. If you bought a GX 550 in late 2023 or early 2024 check with the dealer for any open recall or software update campaigns. The update takes about 20 minutes and is free. Overall the GX 550 powertrain is a legitimate upgrade. It is not just a spec bump on paper. The torque curve, the hybrid assist, and the 10-speed box work together in a way that makes the truck feel more responsive in everyday driving. The downsides are mostly steering feel complaints and the slight learning curve with the transmission logic. Neither is deal-breaking. The fuel economy improvement alone makes this a worthwhile change from the previous generation.
