Glad you decided to drive AND extend the length of your trip. There's nothing like a good road trip.

While I can (and have) drive upwards of 1,000 miles per day on a cross-country mission, for a road trip (in the western half of the country) involving sightseeing, I plan to allow no more than 500 miles per day (and that can even be a bit of a frenzied pace). I just did two road trips this winter.

The first was Simi Valley, CA to Branson, MO by way of Albuquerque, Santa Fe (and a side trip to Bandelier National Monument and Los Alamos), Dodge City, Lincoln (NE), and Kansas City (we were hitting National Park sites along the way to fill out our NPS passports), which (according to Google Maps) is 2,290 miles in 5 full days (including one long stretch the first day from Simi to Albuquerque, 825 miles). That averages out to 458 miles per day, and we were going almost non-stop (only figuring on stopping at each NPS site for 1 hour, although it usually took 2 to feel like we didn't just breeze through it).

The second was from Branson to Little Rock, Vicksburg, Natchez, Natchitoches (LA), Jackson (yes, backtracking), Tupelo, Savannah (TN), Memphis and back to Branson by way of Jonesboro, AR (again, hitting NPS sites for our passports), a 1,541-mile trek in 4 days, for an average of 385 miles per day. That was going from dawn 'til past dusk each day (probably 13-15 hours each day) and stopping two times per day for an hour or two each.

My point in this is, while you can drive ~1,000 miles straight from Joplin (I was just through there in December on my way to TUL, flying back to BUR after those two road trips--I indeed did drive there and fly back!) to El Paso in a hard day's driving, if you plan to see anything on the way, cut that distance-per-day by half. So, I hope you've extended it to at least a four-day weekend!

Like I said, I'm glad you chose driving. Carlsbad is very cool--I went through there probably 8 years ago (though it feels like just a couple) on another NPS-hunting trip (we hit Big Bend, which is very scenic in its own right, and Guadalupe Mountains just across the TX border from Carlsbad, which isn't all that special). Also, since it's on the way, I'm sure you've been to O-City (living in Joplin), but I've been told the memorial at the federal building is quote moving (it wasn't built last time I went through there).

One option no one's mentioned: if you want a unique experience, there's always Amtrak. You can drive to OKC and take the Heartland Flyer to DFW and transfer to the Sunset Limited to ELP (I don't think there's a danger of missing the connection in Fort Worth, as I believe the Flyer trainset gets joined to the Sunset Limited's trainset there). It's a 33-hour, 45-minute trip (including the layover and assuming the Sunset Limited's on time, which is a big assumption, although not as much so westbound), but if it's running on dates that work for you (it's only 3x per week), it's an awesomely fun way to travel! (If you've never done a train trip before, I highly recommend it. And before all you frequent flyers out there flame me, yes, I understand Amtrak's long-distance trains aren't a serious mode of transportation for people who don't want to enjoy the journey along with the destination, but when you've got plenty of time and want a fun, social, scenic, relaxing travel option, nothing beats a good ride on the rails.)

Question (to sundrop): if you chose to fly, would you drive to TUL? I would think fares out of JLN are bad like they are out of SGF, which is why my family in Branson always uses TUL when paying for tickets (and SGF only when using miles). The fact that you'd have to drive the couple hours to TUL only makes it make even more sense to just keep going in the car (especially since you want to sightsee).

And all y'all frequent flyers need to get out on the road more often!