The way you originally wrote about it made it sound as though there were lots of SLC options, but you rejected them simply because you didn't want to be on a 767. You didn't initially mention that they disappeared.

You'll find a lot of "blame the victim" around here. That was definitely a frustrating experience. It sounds to me as if you did just have some really bad luck: a very complicated itinerary, a series of perhaps not-so-great agents, multiplied by DL's hit-and-miss computer system. I'm not Diamond, but others seem to have better luck than you did. (But I wouldn't be mad about their not allowing you to change to the next-day flight without charge--that agent didn't know the whole sad story, and even if she did, it would be hard for her to justify to her boss.)

On the brighter side, how was San Diego once you got there?