Well I didn't get my truck new and been looking at it closely since I got it and think its already leveled... It sits only 1.5 inches lower in the front which is the same as my fathers truck and he leveled his
good news is a 34" tire(275,285/65/20) on a 20" rim is very common so you have lots of selection and as well for the most part you need not worry about a rubbing issues.