General Motors is making sure its next generation of full-size trucks is just right. Although the 2007 GMC Sierra and 2007 Chevrolet Silverado are just six months from the start of production, GM's engineers are still busy working out the bugs. In our latest spy video, our shooters managed to catch a GMC Sierra prototype as it crisscrossed the Rocky Mountains.

With camouflage covering most of the exterior body panels, this prototype didn't reveal any new details we haven't seen before. It's obviously a four-door crew cab, but traditional extended- and standard-cab versions will be available as well. The overall shape of the truck won't change drastically, with most of the changes expected to come in the design of the front end and the interior. We've been told this Sierra will feature more changes from its Chevrolet cousin than previous versions, but all the hardware underneath will remain largely identical.

Both the Sierra and the Silverado will likely offer the same engines and transmissions already being used in the 2007 Chevrolet Tahoe/GMC Yukon SUVs. Starting with a base 4.8-liter V8 with 290 horsepower, the lineup is also expected to include two 5.3-liter V8s and a top-of-the-line 6.2-liter, 380-horsepower V8 on Sierra Denali models. Both versions of the 5.3-liter V8 will have approximately 320 hp and cylinder deactivation for improved mileage, but one will also offer the ability to run on E85.

A new six-speed automatic transmission will be used with the top-notch V8, while lesser versions will use a four-speed auto. Once production of GM's new six-speed transmission increases, we expect it will be offered across the board.

Although our video camera wasn't able to peer into the cabin of the Sierra prototype, earlier pictures of the inside of a Chevrolet Silverado show a much improved interior design. Unlike previous GM trucks, the cabins of the Silverado/Sierra twins will have a slightly different setup than their SUV cousins. Higher-grade materials and all the latest features should make both the Silverado and the Sierra more comfortable and stylish inside. And let's face it, anything is better than the drab, plastic-coated interior of the current trucks.

Expect to see both the GMC Sierra and the Chevrolet Silverado make their official debuts sometime this fall with sales beginning in early 2007.

Riding on the GMT900 platform, the Silverado’s introduction comes after that of the full-size SUVs, and up until this moment - has been very well hidden behind miles of black vinyl. Although this was originally scheduled to arrive as a 2008 model, Chevrolet has been working at a fast pace and the Silverado will likely debut this fall, with production starting as early as October. And, as one can clearly see, this is no Tahoe clone, but a unique look including stacked headlamps, which separate the trucks from the SUVs.

We’re a bit surprised that the Silverado doesn’t have some of the signature styling from the 2003 Cheyenne Concept - such as the wraparound glass at the back of the cab, yet we think consumers will be pleasantly surprised with both the styling and car-like refinement that the Silverado is said to have. And, equipment-wise, this Silverado is equipped with a roof-rack and back-up sensors.