I finished the first draft of the PhD novel a year and a half ago and have been revising it on and off since then. (Lots of stuff has delayed me.) Things that are difficult about revisions:
1. Letting parts of the novel sit for so long that you've honestly forgotten what the hell happens in a section.
2. Not writing down ideas for revision as you have them, thinking you'll miraculously remember when you get to that line or that phrase. You don't.
3. Even after all this time letting a section or scene sit, you *still* don't know what is supposed to happen at the end of the section or scene.
4. Hating it. Like, really and truly hating it.
Case in point: My PhD novel is in five parts, each part a different time period. Each section has between one and three point-of-view characters. For each section I've had to do extensive research into not only gardening history but also food, medicine, clothing, daily lives, women's lives, art, etc., etc. of that time period. My Victorian and Second World War sections were the easiest. The Georgian section was a pain, but it's pretty much finished now. The contemporary section still needs to be finished (I have only recently figured out the end of the whole novel). And then... And then there's the Tudor/Stuart section.
It's my kryptonite. It's oysters and creamed spinach and jazz and horseradish all mixed together. I hate it with the white hot passion of a thousand suns. I have torn it apart, put it back together, torn it apart, changed POVs, deleted whole scenes and storylines, added new ones. For months. YEARS. I was stuck a week ago with these three characters who each had secrets from each other... and then nothing. I had no idea how to fix it, how to end it. So I let it sit and thought about it. I let it sit and did NOT think about it (sometimes NOT thinking about it lets your brain breathe a bit and you come up with the solution).
I finally FINALLY figured it out a few days ago. I've had to get rid of more stuff, bring a long-dead character to life only to kill him near the end of the story. I'm still in the middle of fixing it, and I still hate it, but I think in some way that hate may be because I sort of love it again. Hate and Love are close cousins. The opposite of love isn't hate, it's apathy. So if I feel this strongly about this section of the novel, there has to be a reason for it.
Plus, hating it so much makes me want to finish it and walk away from it. Quickly. Oh so Quickly.
It's not the most efficient way to finish a novel, but it's one way.