I'll vouch for the 22mpg vs 20mpg thing. Last summer drove to maine, me wife and kid in my tacoma, my mom and dad in his '13 gmc sierra. He indeed got 22 and I got 20. Did the math when we filled back up. Must be the 4cyl shutting off at cruise speed. I'll keep my taco for 2mpg is no big to me.
First gen was 95-04 with a refresh in like 2000 right? Sounds pretty similar. Maybe they were waiting to see what the small GM's looked like first. Seems logical.