I have made that trip several times (actually past Dallas second day). But, if you have not done any 800 mile plus days, you should not plan on doing two in a row, leaving yourself the option to stop ANY time you get too tired to keep going safely. Then if you do keep going, that is just fine too.
The fuel stops are pretty far apart from Yuma well into Texas. There are plenty for the LT's range, just be sure you don't ever try to "stretch" it, may have a nasty surprise. Hint: Carry one or two ESR fuel bottles, available at REI, or most camping stores. The one quart ESR bottle I carried really saved my butt big time once! My stops going east were usually Yuma, or Dateland (loved the date shakes there), then Lordsburg, then Van Horn. From there on to Dallas, fuel stops are more plentiful.
There are lots of ideas on how to dress. After a lot of LD riding in all types of temps, I wound up using mesh pants/jacket, with polypropylene (underarmour) underwear under it. That keeps the wind off your skin, and wicks sweat away. If it gets cool (or wet), rain gear on top of that, and if it gets cold, stop and put on Gerbings heated gear under it all.
One thing I found that heps a LOT when it gets hot is neck bands that have crystals in them to soak up and hold water. You can get them at welder's supply houses locally. I got mine at the big welders supply on Clairemont Mesa Blvd. I carried a couple in doubled gallon size zip lock bags (they usually leak at the corners
) Seems the articles are true, keep your neck cooler, which cools the blood flow to your head, and your whole body feels better.