The Sierra has a comfortable ride with tons of room in the front seat and also in the back. I like the short box. It was just enough for everything I was hauling and kept the vehicle length shorter. The 8 cyl give the Sierra great pick up. However the gas mileage is quite low. I have owned it for three years (48,000 miles) and have not had one problem with it.
The seats in the back fold down for cargo space, great for groceries, sports stuff and the family dog.
When I bought it no one made a cap for the short box. They probably have one now.