Flattest, warmest route to Las Vegas in January from NC

I40 has signs that flash for when the snow or conditions get to bad. Should tell you something.
You go over many foothills and mountains on it also.
Bottom line if you want flat is I10.
You do go over some hilly areas as you near Vegas but they are not bad. The only other thing in your winter driving is wind , you are going against it all rgw way. Gas mileage sucks at times.
Have fun
We stay at Arizona Charlies RV park, reasonable and all pull through sites.