When I'm working on a novel, I have a tendency to write short chapters (1k-3k words). This is not a problem, per se, but I sometimes feel the need to have one or two longer chapters to slow down the pacing. I have a hard time doing this in a satisfying way.
In most cases, my novels follow two or three characters or groups of characters. Each chapter focuses on a single character or group, and the chapters are ordered so they rotate between all the groups (so there are rarely two chapters in a row that follow the same group).
I've tried merging chapters by simply concatenating two chapters that follow the same group, replacing the chapter break with a scene break. This tends to feel like two chapters forced uncomfortably together, for obvious reasons. It also usually requires a fair bit of rearranging adjacent chapters to keep a somewhat even rotation between character groups. Combining chapters that follow different groups feels even worse. It stands out as odd when the other chapters follow only one group.
The only other option I see is making chapters longer. I'm hesitant to go down that road. It's not worth adding boring filler to try and get the pacing right, and dropping in five or ten pages of new, compelling material can be extremely difficult, and tends to require adjustments in the surrounding chapters as well.
So, what technique would you recommend for adjusting chapter length?