Yep! Should either put it in your sig or include the info when you ask questions.
New member though so it was easy to poke through a couple old posts and find his truck is an 89 K1500 ex-forest service truck.
There's not really a true all-in-one combination switch like the 1995-up column. The lever on your 1989 model is called a combination lever, sure, and a truck with intermittent wipers does indeed use a different lever - but the actual electrical portion of the switch is a separate piece inside your column and the lever just actuates it.
So you'll need the switch, lever, and the wiper motor itself. Suggest you get the 1991-up design motor as it has the easier-to-repair/replace circuit board for if and when it goes bad.
Not to scare you off from the swap, the intermittent wiper motor does suffer from some issues but rest assured they are ridiculously easy to fix if you're handy with a soldering iron. It just takes re-soldering the joints where the harness connector attaches to the board. Or, even easier to replace the board itself as it's a common issue. (I personally would just fix the original.)
I *think* but am not 100% sure the wiring is already compatible with either wiper motor, but it may take someone with more recent experience to say for sure. It's been too many years since I played with a bare bones model to recall. There were some early GMT400's with a weird little module inline in the wiper harness that may have had to do with intermittent wipers.......anybody else recall that?
Richard