Drive: 2007 Chevrolet Silverado Heavy Duty and GMC Sierra Heavy Duty
By: Mike Levine
© 2007 PickupTruck.com
truck engineers like General Motor’s Jim Mikulec, the man responsible
for component integration in the 2007 Chevrolet Silverado and GMC Sierra
HD pickups, must be feeling like they’re on a treadmill where each
revolution spins a little faster than the last.
when the GMT 800 heavies were
introduced, tougher competition and stricter government regulation
have forced GM’s truck wizards to continuously refine and improve
their product - especially the Duramax diesel engine that’s in its
fourth iteration since we first drove it.
we were in San Diego driving the all new GMT 900 HDs. These trucks ship
with standard 6-speed transmissions and a choice of new 6.0-liter gasoline
or 6.6-liter diesel powerplants. Last year's 8.1-liter big block V8 is
no longer offered. Gone, too, is the option of a manual gearbox.
26 different Sierras and Silverado for us to spend time in, demonstrating
nearly every kind of cab, bed, engine, payload, and towing configuration
you could come up with for these workhorse pickups.
at least 30 minutes and 10 miles in 6 of these trucks through San Diego
County. The terrain almost matched the variety of the trucks. It ranged
from sea level to 5,500 feet over SoCal super highways and two lane twisties
through the high desert.
a silver GMC Sierra 2500HD 4WD extended cab long bed powered by the new
Gen IV Vortec 6.0-liter gasoline V8. It was ballasted with a simulated
2,575 pounds of payload in the box.
curb weight is 3 tons, and its gross vehicle weight rating (GVWR) is 9,200
pounds, so we were about 600 pounds shy of the max GVWR. Even though the
new Vortec is rated a best in class 353 horsepower and 373 lb-feet, the
driver could still feel the burdened response of the engine against the
weighty payload, especially during launch through 3rd gear when the broad
range of the new 6L90 6-speed transmission became a practical advantage.
gearbox is lighter and smaller than the 4-speed 4L80 heavy duty transmission
in the outgoing HDs.
There are two rear axle choices for the 6.0-liter, 3.73 and 4.10. We
were equipped with the stouter 3.73 axle, so no doubt this also contributed
to some of the strain during initial acceleration.
with the standard Z85 suspension package, the handling and steering of
the truck proved extremely capable managing the near full load. While
not necessarily sports car like, steering was very precise and driver
feedback near perfect. This was especially noticeable and helpful on the
surface streets that wind through San Diego’s urban and hilly neighborhoods.
and 4WD GMT 900 heavy duties use recirculating ball steering with a ratio
of 24:1. This is nearly twice the steering ratio of the 2007 Dodge Ram
HD, which offers a 13.4:1 recirculating ball system only on its 4WD pickups.