OMAHA, Neb. -

Billionaire Warren Buffett decided it was time to upgrade his 2006 Cadillac DTS after General Motors CEO Mary Barra pointed out how many improvements had been made since then.

Buffett wrote a letter to Barra praising his car-buying experience at Huber Cadillac in Omaha. GM posted the letter and a story from the saleswoman who handed the deal online at its blog, http://fastlane.gm.com , this week.

Buffett sent his daughter, Susie Buffett, to the dealership to make the purchase. Warren Buffett says the saleswoman did a great job, including recommending that Buffett buy the XTS sedan he picked, not the CTS coupe that Barra had recommended.

Buffett joked that the reason the saleswoman recommended the sedan is that his daughter described the 83-year-old investor who runs Berkshire Hathaway as "hopelessly over-the-hill."