I'm getting to final edits of one of my books. Bear in mind this is a YA action story. I've been cutting long exposition, by request, and keeping the pace up. Making sure each chapter end asks a question to read on for (note, not always a cliffhanger.)
My beginning, though, is not bang-bang-bang. It starts in a house with a conversation between a brother and sister. But the conversation asks questions - what's happened? Why might they be desperate enough to think about stewing a cat? Why are there aliens in the lough? Why have they no roof? It's done all through character experience, it's not fast but it moves through the scene without too much exposition and shows rather than tells a lot.
I have another book I'm working on where slow pacing has consistently been a problem, identified by betas right from the start, and I can see why - the story started at the right place, yes, but it went too fast, leaving me telling back story ( that old exposition) in scenes where showing would be better. Currently, I'm adding in a new section that allows me to show most.
So, pace, yes. But also storytelling - when, how, who, where.
And then there's the trilogy - it has more room to breathe, a little more introspection, more world building but it still has to fight against getting bogged down. And its mc loves exposition and thinking, lots. So in this case, the secondary characters keep the pace up and allow the odd slow down.
I don't think all this can be achieved by internal conflict ( which has the danger of introspection) -
I think something external can be useful to drive the story. In fact, a book built entirely on internal conflict would send me to sleep, I'm afraid.