Marvel, your trip sounds like it could be wonderful!
How much time do you have for your road trip?? Colorado and Utah have some amazing scenery
We did the drive from Denver to Utah via I70 - It's a spectacular drive up through the mountains and past the ski resorts like Vail near Denver. As you approach the western edge of Colorado you can detour via the Colorado national Monument ( near Grand Junction) a spectacular drive up over red rock canyons and peaks. back on the intersate it's not far to Moab which is a great base to visit Arches National park and Canyonland national park nd dead Horse Point State Park ( all spectacular) . Moab is an "adventure" town - sooo many great tours - river trips on the Colorado, back road 4WD and dirt bike trips as well as rock climbing if that appeals to you.
From Moab you could head south to Monument Valley and across to the Grand Canyon, or alternatively, from Monument Valley you could head north up via HWY 95 and HWY 24 , through Capitol Reef national park to pick up Hwy ( Scenic Byway) 12 which will take you down through Bryce Canyon National park and Zion national park and on the Las Vegas. Personally, we were more amazed by the scenery of Bryce canyon and Zion national parks than we were about the Grand canyon - but they may be because we didn't really know what to expect at Bryce and Zion - they were both a jaw-dropping surprise. Bryce Canyon at dawn on a clear, cold morning was one of the most beautiful things I've ever seen .
Scenic Byway 12 is frequently listed as one of the most scenic drives in the USA and I can say that the day we drove from Bryce Canyon to Monument valley was one of the most spectacular driving days we've ever done
http://www.scenicbyway12.com/
Can't help with the Dallas to Colorado part - we will be visiting Southern new mexico for the first time on our upcoming trip, but you will prbably need to head up north via Albuquerque etc ( on my to-do list!)
Will be very interested to hear what your final plans are
Andona