There is diesel at every stop in the park. When I was there last week it was running 2.69/gal
Also I just went from Dayton OH to fishing bridge. We stopped at Custer State Park for 6 days before heading into Yellowstone, so I can't really help you with stops on the way out, but I will say it's a solid 9-10hrs to Yellowstone from Rapid City SD. Highway 16 isn't nearly as bad as everyone says. The east entrance isn't bad at all, the tunnels are plenty big for anything you want to pull through it. From the east entrance it is 53 miles to Fishing Bridge at 45mph..... Plan on 2hrs from Cody to Fishing Bridge.
