Some routing ideas through my neck of the woods (Utah/western CO area)...
SLC to Dinosaur: if you have time, I'd recommend taking Utah 35 rather than US 40 between the Park City and Duchesne areas. 35 takes maybe 15 minutes more, but it is arguably more scenic and has quite a bit less in the way of traffic - especially truck traffic. The Duchesne-Vernal corridor is a significant oil/natural gas producing region and 40 is always filled with tanker trucks heading to refineries in the Salt Lake area.
Dinosaur to Moab: get to Moab via Utah 128. It is far more scenic than 191 between Moab and I-70 and it has less traffic. Coming from Colorado, 128 is only 10 minutes longer than 191 - plus you get to visit the somewhat well-known ghost town of Cisco.
Monument Valley: be aware that at least as of now, a lot of stuff in that area is still closed for covid. That area is all on the Navajo reservation which got hit very hard early on, and they haven't really gotten to reopening things yet. That includes Monument Valley Tribal Park and I believe the Four Corners monument as well. Fortunately, you can see most of the good stuff in Monument Valley just from US 163. Goosenecks State Park and the Moki Dugway in that area are also worth a stop - and if you do the Dugway, you might as well drive a few more miles down the dirt county road to Muley Point, which has panoramic views of the San Juan river canyon with Monument Valley in the background.
Heading east from there to CO: I-70 currently floods in Glenwood Canyon about once every week or two now thanks to a wildfire last summer. US 50 is also closed most weekdays between Montrose and Colorado 92 due to construction (and only one-lane traffic on weekends, I think) so that is a poor detour. If you run into that situation, Colorado 82 over Independence Pass is a ridiculously scenic alternate that should be open unless some idiot semitruck follows his GPS and gets stuck trying to climb it (this has happened more than once). I've never done 160 over Wolf Creek Pass, but from what I've heard it's fairly scenic, and depending on where you want to join up with 70 that might be your best bet.
Sounds like you are set on In-N-Out if you are in SLC but a local place we enjoyed on our 2010 trip there was Ruth's Diner. Also good was Pat's BBQ and Red Iguana (Mexican)
If you do Red Iguana and get scared by the hour-plus wait for a table, be aware that there is a Red Iguana 2 just a block away on South Temple. It doesn't quite have the same vibe to it as the original on North Temple, but they serve the same food there... and you get seated a lot quicker. Ruth's is up Emigration Canyon which is a neat drive if you haven't done it before.
That said, yes there are indeed multiple In-N-Out locations throughout the Wasatch Front. I have never waited less than 20 minutes at any of them.