Just made a trip in August from upstate NY to Mount Rushmore, Yellowstone and Glacier. Stopped in north western Minnesota to visit relatives on the way home. I have a diesel so I averaged 11.2 mpg and I have a 36 gallon tank. Total trip on the truck was 6349 miles. Returned home via northern western Minnesota, Wisconsin, Michigan and Canada.
We were ready to stop every 3-4 hours for a break and fuel. Filled up weather I needed it or not. You'll find plenty of stations to get fuel.
We stayed just outside the north entrance of Yellowstone - wanted full hook ups and was heading to Glacier after Yellowstone.
We stayed at
Rocky Mountain RV Park & Lodging, LLC
14 Jardine Road
Gardiner, Montana 59030
Worked great for us - entered and exited the north entrance each day.
So - keep the rigs you have and stop as often as needed. Never hurts to carry a 5 gallon can of fuel along.
And - 35 foot rig - you may not want to stay in Yellowstone park.
I use an Edge Insight CTS to monitor engine/transmission parameters. Never had any problems with engine or tranny temps during the trip.
I have a Garmin GPS and all of the truck stop Points Of Interests loaded. Also, updated the maps before I started the trip to ensure I had the western states in my GP and most recent "maps".
I use Microsoft Streets and trips to plan the trip before I go and tweak the route based upon our over night rest stops.