"Light trucks" (in the US, at least) don't have to meet the same fuel economy standards as passenger automobiles, the latter of which includes SUVs. So you build a massive luxury crew cab with a tiny, essentially useless bed, and you can emit more pollution than if it had a permanent "cover" and connected the passenger cabin with the cargo area.
My first pickup - 1985 Nissan pickup (manual) averaged 25mpg.
Curious how fuel efficiency holds up over time. Does a 10, 20, 30 year old car averaging 10K miles a year still basically get the same efficiency as a new one?
It can. It would require the engine to be a good production version (which it may be if it has the miles and hasn't already had problems), good maintenance through its life, and a bit of luck. Would most cars, probably not. There's too many variables to cause original efficiency to decline, one big one being typical abuse and neglect.