OK, now I'm a little more awake.
We took I-80 out to CA, then I-90 most of the way back (from Yellowstone back to WI). The truck traffic is significantly heavier on 80. I enjoyed 90 much more. We stayed in Omaha (at a county campground) on the first night west. We stayed in Laramie, WY; Salt Lake City; and Lovelock, NV on the following nights. At Salt Lake City, we stayed at Antelope Island State Park. It's an island in the Great Salt Lake ($10. ). Near Lovelock, NV, we camped at a state reservoir (state park). The county/state parks were nice and also cheap. We stayed at KOA type places too. They're convenient, but pricier. You wouldn't need the hook-ups, so the parks may be a nicer option. Also, a lot of other states don't charge an entrance fee like our WI state parks do.
Coming back, we stayed outside San Francisco in Novato, then we took 80 east. We camped in Winnemucca, NV, then up into Idaho to Yellowstone. Traveling on 90, we stayed with relatives the rest of the way home.
I liked the Flying J truck stops among others. The lowest we paid was yesterday in MN - $1. 43/gal. The highest was W. Yellowstone - $1. 89. Be careful around San Francisco. It can be tough (and expensive!) to find diesel - at least for us out-of-towners.
I can share more detailed route info by email if you want. The AAA maps, tourbooks, and campbooks were great to have. We took our time traveling - about 400+ miles per day on average. It can be done much quicker. Also, I was the only driver on our trip and we were pulling our 27' TT. We kept it down to around 68mph most of the time. The winds can be a real bummer on mileage and comfort - especially with that house behind us. We had a bad cross wind yesterday - until we got into WI - where there were some trees!

I still have to run the numbers, but our average mileage was probably around 9. 5mpg. The final tally will be around $700. for fuel on the whole trip.