You are no doubt right about the emissions, what amazes me is that so many seem to deny the existence of the better mileage in the past. Ford once marketed an F-150 full-size pickup that was EPA rated at 29 miles per gallon highway, I spoke with more than one owner who confirmed figures as high as 27 miles per gallon and yet I cannot find anyone on a Ford lot now who seems willing to admit that such a vehicle ever existed.
In 1984 the EPA scoring procedure was revised to reduce highway mileage numbers by 22% across the board. A 1984 model that had been rated at 29 mpg would be rated at 22 or 23 mpg in 1985.