I would suggest US Rt 160 from Durango over the continental divide to I 25 then US 87 to meet I 40 in Amarillo. Rt 160 is really beautiful and u cross the Divide at >10,000 ft altitude. When I went thru there there was snow under the trees- in June! It is mostly 2 lanes with the occasional passing lane. I'm not familiar with the route south of SLC (US6>US191>US491>US160) to Durango. Nor am I familiar with Rt 87 thru Texas. But by then ur into the wide open spaces.
P.S. Durango of course has the Colorado Narrow Gauge Museum and trains....if ur into that kinda thing.