I've been looking at a new Sierra to replace my 2000 Sierra. After reading some posts on this site, it seems that many people with the 5.3/6 speed auto. tranny combination aren't getting nowhere near the EPA's fuel economy ratings of 15 mpg (15.7L/100 km) in the city. The 4.8/4 speed combination gets according to the EPA 13 mpg (18L/100km) in the city. The 5.3/6 speed combo is a $2000 option here in Canada where I live. So, what can reasonably expect to get in the city for fuel economy with the 5.3/6 speed combo? Is it worth it?