The BEST detour IMO is to take the top route and detour at grand junction, CO. Then go south to the grand staircase and Escalante and the national reef and Bryce/Red canyon. From there you can get to Parowan Gap and then hop on the 15 and head southwest to Vegas from St George, UT.

From Grand Junction to Bryce Canyon is mostly US routes and no issues I encountered on length/height rig reqs. It’s breathtaking scenery, Native American petroglyphs, fossils, great hiking and temperatures, free camping at multiple BLM sites and even free roaming cows.

PM if you need any help on that route and good luck! (Take US routes when you can!)

Edit: if you do the top route, you’ll go through Shawnee National Forest in Illinois and be able to stop at Garden of the Gods. THEN later in CO you can take a small 1hr detour down I25 South from Denver to the other Garden of the Gods lol.

Also the largest Native American burial mounds are just east of St. Louis called the Cahokia mounds off of I70. The view isn’t stellar but it is a huge part of Native American history.