Thanks so much for your informative post. My studs indeed are
irregular. My thought was to use full sheets untill they because
irregular in the spacing, then cut the sheets to fit the rest of the
studs. I never thought of your idea on the 1x3's but one problem I see
is the outlets would be way recesed if I used those.

As long as the stud spacing is less than 24", the irregularity wouldn't be
a big deal. You could add a stud where needed (sideways if you need to
clear existing wires or something) so the edges of all sheets are
supported. Just cut the stud to length, then use 3" deck screws at the top
and bottom to secure it where you need it. It's not structural, it's just
support for the drywall.

Don't cut any sheets to width until you reach the end of the wall, so every
joint is tapered edge to tapered edge. You can make marks with a pencil at
the floor and ceiling where the studs are located so you know where to
drive screws, or just use an electronic stud finder.

Alternatively, instead of placing 1x3 strapping horizontally on face of the
studs, you could install 2x4 blocking "between" the studs every 24" or so
(flat side facing out). Of course, this would probably be more work than
just adding an extra stud where needed. We used this approach in our master
bedroom so we could install T&G pine vertically on the walls, but it's more
than likely overkill for sheetrock. The only potential advantage would be
solid blocking behind the sheetrock for mounting shelves or whatnot.

Anthony