At 4 full days, you've got much more time to do a little exploring, and that will have some impact on where the best places to stop would be.

For example, I'd consider spending your extra time at Arches or Canyonlands National Parks. So you'd still go to Richfield UT the first night, but have a shorter day to perhaps Grand Junction CO on day two, and then make your final night in Kearney NE.

That's not to say that's the best choice, its just one of many options. You'll have to decide on where you want to spend that extra time. There are lots of other parks and places, with Utah and Colorado having some of my favorites. You also wouldn't be limited to having to go to the most direct route. For example, you could also reasonably detour up to South Dakota and see Mt. Rushmore/the Black Hills, or the Badlands. When you are planning, figure you can reasonably drive up to about 600 miles in one day, and if you are going much beyond that point, you could be in trouble.

Mind you, you don't have a ton of extra time, just time enough to give you options. The weather also could be a big factor which could delay you and take away any extra time you have.

Fuel costs will depend upon your vehicle, but RTA's Fuel Cost Calculator can help you figure out those costs. You can generally find a motel for about $50 a night, but RTA can also help you there too through our booking service. You'll find links to both up on the upper right side of this screen (next to the forum text, below the green title bar.)