We've been hearing plenty of horror stories this past week about people trying and failing to trade in their vehicles under the Cash for Clunkers program. We recently received an e-mail from a reader named Rex asking about his particular case. Unfortunately, a big part of the problem is either lack of information or inaccurate information on the part of both dealers and the government. In Rex's case, he was trying to buy a 2009 GMC Sierra half-ton pickup with a 5.3-liter V8. His initial rejected trade was a 1985 GMC Suburban. After that, he was given two different government numbers to call and no one at those numbers or at the dealer could explain why he was rejected.

The answer is actually quite simple. The 1985 Suburban is rated at 13 mpg combined and the base 5.3-liter 2009 Sierra is rated at 16 mpg combined. To qualify for the clunker rebate, the new vehicle must get at least 4 mpg more than the old one. In this case, if Rex had opted for the Sierra XFE, he should've be able to get the rebate because it is rated at 17 mpg, thus clearing the lower limit.

After the 1985 truck was rejected, Rex offered up a 1990 3/4 ton pickup (example above), which was also turned down. The explanation here was also mpg-related, but for a different reason. The larger, newer truck is a heavy duty unit with a gross vehicle weight rating (GVWR) of over 8,500 pounds. These larger trucks are not subject to CAFE standards and aren't assigned EPA sticker ratings. Without an EPA sticker value, even though this truck is considerably thirstier than the Suburban, it was also turned away.

The moral of the story is to make sure you carefully check the mpg rating of your trade-in and the new vehicle you want to buy before you go shopping. For trucks, the improvement must be at least 2 mpg for the $3,500 rebate and 5 mpg for the $4,500 (for cars: 5 mpg and 10 mpg). You can do the research by visiting fueleconomy.gov.

[Photo by Ethan Miller/Getty]