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WATCH: Inside General Motors' Top Secret Extreme Vehicle Tests

ABC News(NEW YORK) -- General Motors is putting its vehicles through a series of extreme tests in a bid to make sure the cars -- and the company -- last.

The grueling tests come after bankruptcy and a government bailout left American taxpayers with ownership of a quarter of the company.  GM's stock price has slumped so the government has been forced to hold its shares rather than sell them at a loss.  The extreme testing is an attempt to strengthen the company's vehicles -- and its share price.

The newly restructured GM granted ABC's Nightline unprecedented access to its super secretive testing facility, called the Proving Grounds, in Milford, Mich., where it allowed cameras to film new models being crashed, flooded and pushed to the limit in severe environments.  Many of these tests had never been seen before by the public.

GM was once one of the biggest players in the industry, rolling out iconic Cadillacs, Chevrolets, Buicks and more.  But the company became bloated and during the recession, it fell into bankruptcy and needed a government bailout.

"This company is under tremendous pressure to deliver great products and great profitability -- and quickly -- and the pedal is to the metal, so to speak," said James Bell, head of consumer affairs for GM.

Bell was Nightline's tour guide for a wild ride through a series of breathtaking tests.  In one test, GM dumps a "lifetime of rain" on a vehicle -- nearly 7,000 gallons in eight minutes -- which tests how well the engine, electronics and other components stay dry.

In another, engineers drove a truck into a "dunk tank," then deliberately flooded it to see whether the truck's undercarriage would withstand dangerous corrosion.  For yet another, they drove a vehicle at an impressive clip straight into a flooded road to see what would happen if a driver ignored safety warnings and did just that.

"Sometimes floods happen in this country, so we know that these vehicles are going to withstand that," Bell said.  "We're doing above and beyond what the government requires."

For the first time ever, GM allowed cameras to film inside its climatic wind tunnel, capable of creating Arctic cold one day and desert heat the next all to see how vehicles do in extreme conditions.  In another first, General Motors allowed Nightline's correspondent to drive onto a test track to see if a Chevy truck could manage massive pot holes and ditches so deep, their size is a trade secret.

The now leaner, meaner, post-bailout GM believes its tests are working, so much so that this summer the company staked everything on an unprecendented money-back campaign.

"If you're not happy with your new Chevy, return it," the company's commercials boasted.

But despite its vigorous testing, General Motors just last month recalled over 40,000 vehicles over potential fuel leak concerns, according to a National Highway Traffic Safety Administration report.  

And Consumer Reports ranked GM 12 out of 13 car companies for reliability in its most recent list, noting that models designed by the "old GM" are dragging the automaker's score down.

Chris Perry, GM's vice president of U.S. marketing, said the company's process is improving.

"We believe in the products we're developing," he said.  "[And] we're saying 'hey, you know what, we recognize the ills of our past, but do yourself a favor and compare us again.'"

Copyright 2012 ABC News Radio

ABC News Radio