Intermitent wipers; really intermitent

Seems to be no rhyme or reason to when the wipers work accurately/choose their own speed/don’t work at all. Only thing that is fairly consistent is that they will work correctly, for a while, while the engine is cold.

Do I need a new wiper motor assembly, wiper selector switch or both?

1997 Chevy S-10 2WD, 6 cyl.

With a GM vehicle this old, the first suspect is the multi-function switch in the steering column.