Buy a national parks pass. For $80, you will save a couple hundred $$ on admission fees. You don't state how old you are but, if over 65, it is even cheaper and gets you 1/2 price camping in most federal campgrounds.
You have no budget for maintenance. We have a line item for this in our budget and all maintenance and repairs are included - not just for the vehicles. Besides oil changes and tires, you will probably replace water filters, light bulbs, outside chairs, pots, etc.
Your restaurant budget is really low. You have no clothes/gifts/souvenirs budget. But, your admission budget is really high (unless you plan to raft the grand canyon) so some of that can be diverted to other things.
I'm not sure why you are including health ins., wireless, and dish, unless you are paying extra (over and above what you normally pay) during the four months of travel. If not, they aren't expenses due to travel.
I'm not sure how you are calculating your fuel budget. Typically, we drive our bus, park it, and go explore in our jeep. A 5200 miles bus loop means we put at least another 5200 miles on the jeep. At $2/gallon, your budget would only cover our bus fuel. Even if you get 10 miles/gallon, at today's current average of $2.25, you aren't covering much more than place to place fuel. And the price will be going up over the summer.
We have been fulltiming for about 2.5 years now and keep close track of our budget. That said, we average $2500/per month in traveling expenses (sites, food, gas, maintenance, propane, attractions/gifts/souvenirs) and we don't scrimp on what we want or do. I think your overall number is good, I just think you will find the $$ amounts a little different than projected.
Best of luck and I hope you enjoy your trip! It is a beautiful country out there!
