We've done I-10 to SoCal many times. Easy route from Phx. to Las Cruces & on. I-40 from what I remember, a little more grades to do, more truck traffic it seemed, but not a bad route. There shouldn't be any grades which would be very severe (not with your rig), I would think.
It would depend on what you guys want to see. Might go out one route, came back the other.
Here a somewhat recent post with info on both:
Sights & Sites I-10 South & I-40 North AZ & NM & I-10 in Texas.
San Antonio & the Hill Country is a neat part of Texas. Goliad/Victoria would be south of Houston, but I liked Goliad & the area when we stopped there. Lot of History happen there. Rockport & Corpus Area (south of Victoria) are neat areas as well. Texas Coastal Bend.
This one may have the same info, but perhaps has something different as well, Just In Case:
:h Ditto It does have Sights & Sites for I-25. One can also go to Santa Fe, then drop down using "Back Roads" to pick up I-10. US 285 can take you from Santa Fe to Carlsbad & on into TX to I-10 at Fort Stockton; or to US 90 which can take you to San Antonio, TX & keep off the 10 where it has the 80 mph speed limit. However, using 285 all the way would keep you out of some of the more scenic sections of NM.
We use US 285 from Santa Fe, but a little after Cline's Corners (I-40), we use NM 3 to US 54 to Carrizozo. US 54 S turns into or joins US 70 on it way to Alamogordo. From Carrizozo, one can branch off to see the mountains of Lincoln Nat'l Forest via US 380, keep on 54 to Tularosa & take US 70 to Ruidoso, or go on to Alamogordo/White Sands. Etc. Many options.
Here's a link (someone going from Houston to Los Angles: My info is the same, but it has other
Comments & Suggestions.
Some Really neat things in AZ & NM, IMHO. But most are off the Interstates somewhat, not all. Same in Texas.
