I find the contradiction in the killer's strategy to be odd here. If this is indeed a disguise - and I, along with others, believe it is - they didn't want to be recognized. And yet, they didn't seem to have any issues with the vehicle being seen and possibly identified. Nor possibly Elizabeth recognizing it either.
Was this someone Elizabeth might have known and recognized and the disguise, if there was one, was to conceal their identity along with the darkness until it was too late? Maybe someone, not necessarily a well known acquaintance to Elizabeth, that she had a one time issue with in the past? Someone she would have recognized and been immediately alarmed, but didn't necessarily know his/her name? I'm guessing this disguise was not necessarily good enough to work in the daylight, but with the darkness was good enough to allow them to get close without causing concern. Of course, such a disguise may also have been for the benefit of any neighbor who stepped out or looked out a window.
If the disguise was for the purpose of negating an accurate account from witnesses, then the truck would surely be available for description by witnesses. And yet, there it is on video even down to the make/model with the decal. And it is seen the night before as well. A pick-up is not uncommon in the south, especially Texas, but that truck is distinctive enough that a connection could be made if this was someone Elizabeth knew, either directly or indirectly. Borrowing the truck, even if the person wasn't told about its intended use, leaves open the possibility that third party might make the connection. I had to rent a vehicle through a major car rental company once and all they had available was a pick-up truck. I was surprised as I never knew of such a vehicle being available through an Avis, Hertz, Budget or other such agency except for one local area of the country near me. (That one particular area has a popular outdoor area only available if you have a 4-wheel drive and there are one or two specialty places nearby that rent such vehicles.) Even if rented, that also carries the risk of a third party making the connection. That leads me to believe this vehicle is likely owned by the killer. And if this person was hired to do this a connection is less likely. A hired killer is not necessarily a 'professional' like seen in movies or TV, but could be someone who needed or liked to have the quick cash.
Just thinking out loud here.