I can't explain the truck, but it doesn't take much money to buy an older one.
The girlfriend in California comment isn't surprising. If this is Brian, the only thing that is curious is why he didn't refer to Gabby as his fiancé.
The Yosemite text message has several possible explanations. One of them is a storyline Brian is creating. He and Gabby argued and decided to separate and meet up in California. He's reinforcing the story when he shares it with other people.
If what Gabby's friend Rose Davis said is true, that Brian would sometimes hear voices, Brian's way of thinking and his ability to build a story that makes sense, could be fractured.
I see Brian as a deep thinker and someone who is fond of words, but he prefers them in a book. Socially he probably experiences constraints on his ability to communicate in a way that makes sense to others. I'm like this, too. I open my mouth and mischaracterize or misrepresent what I'm trying to convey. I can be articulate and intellectual, and also stilted and awkward.
Stress and anxiety can lock me inside my head, and when I try to speak I'm sometimes only able to provide a skeletal outline of what I'm wanting to convey.
"My girlfriend and I got into a fight. I need to get to California."
"My fiancé is back at the van doing work. I need to get to the van."
MOO