General Motors announced that it will temporarily halt production at its Fort Wayne plant in Indiana for the week starting November 7, in order to reduce its inventory of pickup trucks models.

This is not the first time that GM has stopped production at the plant where the Chevrolet Silverado and GMC Sierra are manufactured. Even though pickup sales in the US have increased from January until August by 9% to 1.1 million units, compared to the same period last year, GM seems to have badly misjudged demand for its models, resulting in an inventory of 122-days.

And this despite the fact that both Silverado andSierra sales have so far increased this year, by 7% and 18% respectively compared to 2010.

GM executives seem to have overestimated demand, increasing the two pickups inventory far more than the 80-days standard for the industry.

So far, the Detroit automaker’s efforts have yielded a small inventory decrease, to 115 days.

About a year before General Motors entered bankruptcy, various reports claimed that the automaker postponed the next generation of the GMC Sierra and Chevrolet Silverado from 2012 to an unknown future date. It wasn’t big news at the time, since the well-liked trucks were only two years into their production cycles, not to mention that high gas prices were limiting the appeal of trucks for recreational buyers. But now that we’re half way through 2011, truck buyers are most definitely back in the mix, and The General may be looking to speed up the timeline on the next-generation model.

Automotive News reports that GM’s U.S. sales boss, Don Johnson, revealed that the truck plants would be re-tooled during scheduled shutdowns in 2012. If GM were to begin building Silverado and Sierra trucks right after the retooling takes place, that would make the trucks 2013 models. But sources tell AN that the retooling will take place throughout 2012, and that the trucks likely wouldn’t be built until calendar year 2013, making them 2014 models.

The news corresponds with comments made by The General’s VP, Mark Reuss, who said in January that some truck programs would be accelerated. But in April, GM CEO Dan Akerson said that trucks wouldn’t be accelerated in a mileage-sensitive market, so it’s difficult to discern exactly which direction GM is heading.

GM hasn’t been very forthright with the amount of changes scheduled for the next-generation trucks, though the expectation is that the updates will be substantial. With 2016 fuel economy regulations right around the corner and the recent resurgence of $4/gallon gasoline, the new pickups will definitely need to be lighter and more efficient.

Word on the web is that the GMC Acadia is back on the chopping block. You may recall that the big crossover found itself in dire straits once before when the entire GMC brand underwent a strategic review during the General Motors bankruptcy proceedings. After that brush with death, the decisionmakers at the company decided to give the entire brand – and by association, the Acadia – a stay of execution. Now a new report suggests that the next-generation Acadia may be scrapped to reduce product overlap within the GM dealer network.

General Motors currently produces three Lambda-based crossovers – the Chevrolet Traverse, Buick Enclaveand the GMC Acadia – and the company says that it wants to keep overlap to a minimum for its Buick-GMC dealers. The next-generation Lambdas are expected in 2014 as 2015 models, but even if the Acadia gets axed, it’s likely that GM will still keep a trio of models based off of the three-row platform, only with Cadillac getting the third model instead of GMC.

Cars are cool, but we certainly love ourselves some big, bad, hardcore pickups – you know, like the Ford F-150 SVT Raptor. General Motors’ conceptual answer to Ford’s desert-blasting pickup is this, the Sierra All Terrain HD concept, which we’ll be seeing for the first time at the Detroit Auto Show next week.

GMC’s brutish pickup relies on The General’s 6.6-liter Duramax diesel V8 for power – 397 horsepower and 765 pound-feet of torque, to be exact – and higher ground clearance, a wider stance and serious suspension upgrades make the All Terrain concept capable of storming through, well, all types of terrain.

Word on the street is that if GM gets up the gall to produce such a truck, it will likely be outfitted by a second-tier firm outside of the GM production lines (like a Roush F-150, for example). Regardless, we want this thing to be built, and badly. See a whole slate of new high-res photos for yourself in the gallery below. Oh, and don’t forget about the Ram Runner, Chrysler’s foray into the niche.

If you think the Ford F-150 SVT Raptor is too hot yet the Dodge Ram Power Wagon is too cold, General Motors’ latest concept might strike you as “just right.” This, the GMC Sierra All Terrain HD concept, looks to bridge the gap between the two hardcore pickups from GM’s crosstown rivals, while still offering top-notch levels of power, refinement and technology.

The four-door 2011 Sierra HD underpins the All Terrain concept, and power comes from The General’s 6.6-liter Duramax diesel V8. A six-speed automatic sends the 397 horsepower and 765 pound-feet of torque to all four wheels. Versus a normal Sierra HD, ground clearance has been increased by about three inches, width has been bumped up to 73 inches (four more than normal) and the whole package rides on 20-inch aluminum wheels wrapped in 35-inch BFGoodrich KM2 mud terrain tires. Off-road performance is enhanced with the addition of Fox off-road shocks (just like the Ford Raptor).

Inside, GM has fitted the All Terrain concept with a Denali-spec interior with additional satin metal finishes and a leather-wrapped dash. What’s more, a next-generation stereo system with an 80-gigabyte hard drive has been fitted inside this concept, and we’ll soon be seeing this new system across the full GM product range.

Currently, there are no plans to create a production version of the All Terrain concept, though GM tells us that if a road-ready version of this ultra-tough Sierra is produced, it will likely be crafted with the assistance of an aftermarket company. We’ll be seeing the All Terrain concept in person at the Detroit Auto Show in just a few weeks, but for now, click through our high-res image gallery below, or follow the jump for the official release.