I love car trips, but I wouldn't attempt this in just a weekend. Also, having lived in NM & West Texas for the last 35 years, I'm afraid you're likely to be disappointed in Truth or Consequences. Carlsbad is nice just for the Caverns, and the best way to enjoy them is take a full summer day (great escape from the heat), walk down instead of use the elevators, and stay until after the bat flight at dusk. Last, but not least, is the fact that the area is not really very scenic - rather flat, brown, treeless, full of scrub brush and occasional oil wells (though it's pretty nice around Cloudcroft, especially as you drop down into Alamagordo).

Best of luck, just don't see how you can fit these into a weekend.