Anyway, the impression I got from a Dodge forum that I frequent is that the daytime speed limit is still 80 on the interstate and US highways.
Oops! Too late to edit, but as I thought about what I typed, I got that part a bit wrong, and a google confirmed it:
daytime AND night time on interstate is 80 mph
daytime on two lane highways (not just US highways) is 70 mph, and night time on those highways is 65 mph.