It took awhile, but GMC and Cadillac's exclusive on the 420-horsepower truck motor is over. Available only in the new Tahoe RST and backed by a 10-speed automatic, the 6.2-liter V8 makes this the fastest Tahoe ever, with Chevy claiming 0-60 in 5.7 seconds. That being said, the tires are good for only 130 mph and the limiter is lower than that, so you still can't outrun a 5.3-powered PPV.The Rally Street Truck package for the Tahoe or Suburban is only a cosmetics bundle, including wheels and tires, with blackout and color-matched trim replacing chrome, new grille and badges, and Dueler Alenza HL P285/45R22 110H tires on the unique wheels. We like the subtle improvements, which aren't overwrought, but to each her own. The RST package is available on 2WD or 4WD models, and none of the mechanical options affect the tow ratings, which are greater than 8,000 pounds.Optional on the Tahoe but not the Suburban is the 6.2-liter engine package. For a reasonable $2,800, it adds the 420-horsepower engine with 460 pound-feet of torque, the 10-speed automatic, 3.23: 1 gears, integrated trailer brake control, two-speed active transfer case on 4WD, big alternator, and most important, magnetic ride control damping with a performance tilt. You can also get Brembo-supplied 16.1-inch front brakes with six-piston calipers for $2,795 (which are also offered on the 2018 Yukon Denali ), and a Borla exhaust Chevy says adds 7-10 rear-wheel horsepower and 28-percent more flow. At certain throttle settings it adds about 28 percent more noise, too.Hammer the gas and the 6.2 bellows, launching the Tahoe forward with barely a chirp (in 2WD). The sub-six-second 0-60 mph time feels entirely plausible, but when at that magic number we wondered what will I do with the other eight gears. It's conceivable you can use any of seven gears at most road speeds, and the shifts are quick and clean regardless how many intervals are skipped, so the nominal 1,500 revs between peak horsepower and peak torque are largely irrelevant. EPA city ratings drop by 2 from the 5.3 but highway numbers are identical, and ours showed 21 against EPA's 22 estimate.Our ears still find the 5.3 a mechanically sweeter, more refined sound, but at these cruising revs it's more likely audiophiles will detect V4 operation instead of raucous sonority. The Borla exhaust sounds authoritative at moderate to wide throttle application before settling into background noise, though it should be noted our rear seat passenger announced unprompted that after 45 minutes he'd tire of it. You might, too, towing a trailer up a long grade.The marriage of engine to gearbox is very good, with only one awkward shift felt where traffic couldn't work itself out, and going from D to M at highway speeds generally dropped it into 7th. In gentle highway cruising the tach occasionally fluttered in the 1,100-1,300 range, which we'll attribute to converter locking as the V4 icon was dark.The steering feels heavier than other recent Tahoes, even those fitted with dealer-installed 22s of the same size, and the damping calibration is definitely firmed up yet there's no pogo-sticking on interstate slabs or jolts. Ultimate grip may be up slightly, and improvement increases the poorer the road surface gets because MRC is so much better at keeping tires in contact. We're torn as to whether the added performance benefits outweigh the rubber-band-tire drawbacks. The brake pedal may have slightly better modulation, at least deep into the travel, than the standard arrangement and the huge increase in swept area should cope with those iffy trailer brakes better, but rush-hour Dallas traffic offered no investigative options.On a 4WD Premier Tahoe the RST pack is $2,630, most of which is the wheels, the 6.2 performance pack $2,820, the front brakes $2,795 and a few sundry upgrades brought the total to just shy of $79,000. For quick reference that's about the same as a base X5 50i M Sport, $5,000 less than a GLS450, and $8,000 more than a nicely fitted Durango SRT ... none of which tow or carry as much. A Platinum Expedition with 400 hp and 480 lb-ft, that tows a thousand pounds more, is similar money.