Thank you for your service and protecting our freedoms.
Having recently completed the same trip you're planning, I suggest you stay north. We went thru Montana, visited Custer battlefield in Hardin, MT, then onto the Mt. Rushmore in South Dakota. From there we followed I80 to I29 and then south to Springfield, MO. We went to Nashville, lots of sights there and then onto Biloxi, MS to visit family stationed there. We came home across I10 to California. Most of west Texas was boring. Cali's I5 is better then the past but still rough in places. Good luck, in this heat I would avoid Cali, AZ and New Mexico. It will be hot, very hot.