Dave Grohl's mom has been hitting the promo trail hard to promote her new book "From Cradle to Stage: Stories from the Mothers Who Rocked and Raised Rock Stars". And it doesn't hurt to have her son Dave Grohl along for the ride to help spread the word. The clearly close pair went on The Late Show with Stephen Colbert this week, after a highly entertaining 6 minutes where embarrassing photos and an old report card are pulled out, the tone becomes somber as the Grohl's talk about the effect of losing Kurt.