What would cause a c6 not to downshift into first gear and start out in second after highway driving? It's intermittent did it all day Saturday but not any ore so far.

 

A sticky/dirty governor will cause that - I've had a couple do it.

The easy fix to try first, is find a suitable area or empty piece of road & give the truck a good fast drive in reverse.

This flushes the tailshaft housing (& governor) with fluid & often solves the problem - it worked in both cases for me.

 

Thanks I'll try that

 

that trick has worked for me as well, another thing to try is to manually shift it.