I think you may be hitting a segement limit problem in NA.

LAS-HOU is going to be 2 segs - via DFW.

HOU-Carribean is going to be 2 segs each way (assuming you want to get back to HOU). That would make it 7 segs already. You will need to cut onw out or buy an extra.

If on the other hand your 'destination' is LAX (given that LAX-AKL is going to be thrown away) then you could do:

DFW-LAS-DFW-HOU-DFW-XXX-LAX

to keep you within th 6 segment limit. XXX would have to be something in the carribean which has a single flight number service to LAX - the only one I know of is SJD.