Brian,
I'd agree with your numbers with a 700r4, 3.42 rear and 28 inch tall tires should easliy produce 16/20, but Dale has a 3.90 rear, to get the same gear ratio as you he would have to be running a tall tire.
I know everybody's engine is slightly different and therefore gas mileage varies.
Also, sometimes people forget to correct their speedometers for changing tire size.
Chris
