The preproduction stuff seems to still be fetching good prices still, although most lots seem to have stayed at the low end of their estimates. Maybe that says more about Prop Store's estimates than the market? :?
As for the regular stuff, it definitely feels like the demand has slowed. I think we're a year or so past peak interest. A lot of collectors have the bulk of their collections together now since the great Disney-fication of late 2015. Personally speaking, my vintage pickups have really slowed in the last year or so and I'm looking to other eras to collect.