Don,
If you are looking for the least elevation changes then I would suggest going the other way through El Paso to Hwy 62/180 toward Carslbad NM. You would then continue on the same road through Hobbs, NM and then on toward Lubbock. This route is very flat the entire way except for the portion through the Guadalupe Mountains National Park where there is a significant elevation gain through the pass. This is all over within a 15-20 distance and then it is all relatively flat again.
Totally different scenery this way of course, all open desert grasslands and salt flats with some really spectacular views of the Guadalupe Mtns and of course you will go past Carlsbad Caverns as well. Both of these are worth a stop if you have the time and have not ever been there.
Your other choices both go over the mountians and are more of a forested route until you get over them. Once on the East side you are again in the flat country over to Lubbock.
Hope this helps, please ask if you have more questions.
Terry