Devil's Tower is a must and then the drive over the Bighorn Mtns. is grand. I'd sprint through Yellowstone and head for the Tetons if it were me. There are some easy backroads off to the east of the main road around the visitor center. Lots of wild life, small lakes and privacy.

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89 300E
79 240D
72 Westy
63 Bug sunroof
85 Jeep CJ7
86 Chevy 6.2l diesel PU

"The object of life is not to be on the side of the majority, but to escape finding oneself in the ranks of the insane."
Marcus Aurelius