Our friends are traveling in a US plated pickup truck and hold temporary residency papers, with a year to go. They are coming from the Pacific Northwest. They live in Zihuatanejo 6 months a year and have for a number of years and are traveling with an older pet.
The stretch north of the state line between Sinaloa and Sonora really really sucks but fortunately is short, even shorter than last year. They are in the process of replacing it but it's BAD. It'a been that way for a long time, but in June, we were ready for it, and kept track. We ran 10 MPH through that stretch. They are replacing it, but not in a manner that allows them to switch from one side to another.
We have always found that if there is going to be a bad stretch of road, it's going to be at or near a state line. Our theory is that they don't really want to claim the "line" so leave a several kilometer stretch on each side untouched. We have seen absolutely HORRIBLE stretches like that.