It's very common for the middle of a project to suck. As writers are wont to do, it's a prime time to be lured to a new, shiny project and abandon the one that's not fun at the moment. But what the pros have figured out is that if you can wade through the slog of the middle, it gets fun again. (or if not fun, at least interesting.)

Who told you the first 80 pages were rotten? I personally don't show anybody works in progress because other people generally eff things up in my head. Much better to write without those influences.