I really feel like he might be connected to NYC. I find the date being 5 days after 9/11 to be a big clue. He could have worked in the tower and either made it out or just didn't get into work that day. He could have seen some horrible things or lost friends, remember some companies were almost completely wiped out.
After 9/11 the death toll was reported in the tens of thousands at first since 50K worked there and all the emergency workers. He could have worked there and seen this as an opportunity to disappear like some may think, almost 1000 people have not had any remains identified that died on 9/11 so it's possible. That could explain him buying the paper, maybe he wasn't finding much on TV about it, and wanted to read the paper to see how things were going.
And what better way than to go 3000 miles away to the other side of the country. I think along the way he stayed at or near that motel in Ohio where he listed that address when he signed in. He was traveling west and stayed there and maybe thought he should have a real address so the owner didn't get suspicious.
His weight also is surprising, being 6'1 and 140 would be sickly thin, I am 5'9 and 155 and people tell me I'm to thin! I think he was probably depressed beforehand, this probably pushed him over the edge if he lost a family member or friend, could have lost his only family member, just 1 parent or all he had was a brother or something, if he didn't work there directly. Also living in NYC could be hard to tan. If you work, that only leaves the weekends, and going to the beach on the weekends here is crowded, there Central Park but maybe like me he's a little shy about tanning in public.
Also one scenario I thought was that he could have graduated the previous summer, got the job in the tower (so no time to tan and enjoy the summer) but that wasn't working for him, could be that it wasn't fulfilling, what he thought it would be, or was to hard for him. Also he could have moved to the city and living on his own maybe his food budget was smaller or he couldn't cook so well. (I'm actually describing myself here quite a bit!)
Could he have gone cross country by bus in 3 days in order to hit his motel by 9/14? Not familiar with buses like Greyhound, but I doubt he flew with the way things were after 9/11 and he could have driven part way and than got on a bus, but that doesn't account for the car, if someone were looking for him, even if he drove and than sold the car, they would still be able to track down where it was sold. So I think he would have taken a bus, not sure if that is possible though?