You might be overstuffing sentences to get it all in quickly. The action. The info. The setting. The revelations. This can lead to long, complex sentences with multiple actions, heavily modified nouns, interruptions, and copious commas, em-dashes, and parentheses. Example: “Digging my hand into my pocket, I ran to the huge, double-bolted, metal doors—just installed last week by my ultra-paranoid, hippie parents—hoping desperately that I could dig out the ancient bronze key in time.” That might be fine amongst a variety of sentence lengths and styles (such as a direct statements or fragments). But sentence after sentence, page after page…. It’s a lot of work for a reader. Slow work. And it’s hard to pick out the most important action; everything has the same weight. Thus, dense text can feel flat. Increase sentence variety to create rhythmic ups/downs. Make some things stand out while others float in the background, creating depth. If a detail isn’t vital, ditch it. When using opening clauses, avoid repeatedly piling action upon action. Lastly, go easy on the adjectives. Inform, don’t bury.