We've been going in Oct. for years.
It used to be a really nice, quiet time to go, but I think the gig is up.
It's been fairly busy our past few Oct trips, and last year it was just CRAZY busy!
You might want to check the dates for UEA (Teacher education, student holiday for Utah schools) if you hit those dates you'll definitely know it.
Weather is usually great in Oct.
DH and DS go with shorts, it's usually a bit cool for me to do that, but we're coming from weather that is probably 10-12 degrees warmer on average, so 76 can feel downright chilly to me.
Definitely plan on bringing along a lightweight jacket for layering as it can be cool in the mornings and evenings even if it gets up to 80 or so during the day.
Don't want to scare you with the crowd stuff - just be prepared since crowds are a possibility that time of year.