I have an 01 SR5 that got 21 mpg before I blew the head gaskets from overheating it due to a bad radiator cap and a 98 that gets 16 mpg by the odometer but it has beefier off road tires and the 01 has stock size tires which are more road style. I figure the tires make a lot of difference plus there's probably a difference in the calculation. It may pencil out to 16 but in reality due to the larger size tires it may be 18 or 19.

Then there's tire pressure, quality of gas, air filter condition, new plugs in the 01, etc. etc. Just lots of variables. If I were to take a longer trip in the 98 I'd probably up the pressure from 32 to 36 psi even though the ride would be a little rougher just to get a couple mpg's better.