We fly United almost exclusively and only got moved once. I called them on it got my original seats back. We always fly in what United calls economy plus, which gives you another six inches of leg room. Doesn't sound like much, but when you're 6-2 and the rude ####er in front of you flops the seat back into your knees it makes a huge difference. Generally costs about $80 per seat more.
Not a big deal, but we always arrive at Fresno about 1.5 hrs. early which is plenty except when the early-late evening flights to Mexico are departing. Give that new parking garage near the terminal a try. If you can score a spot it's so close to the terminal.