Among the best maps available are those from AAA (free to members). If you are not already a member I would urge you to take out a roadside assistance membership before this trip. It could pay you to take out a premium membership. Small price to pay for peace of mind in the case of any breakdown along the way. Great help not only for mechanical breakdowns, but should you have a flat tyre or lock your keys in the car.
You should get a map of the complete USA to give you the overview you so obviously need. Then get a map of every State through which you will be travelling. It is also handy to have a detailed map of places like New Orleans or any other major urban area you will pass through. All free from AAA to members.
Whatever you do, do NOT rely on your technology alone. Many have done so at their peril. Good paper maps and the ability to read them should be your primary tool for navigating.
Lifey