So, according to the original dealership vehicle pamphlet, my 1999 Toyota Tacoma 2WD 4-cylinder 2.4L has a rated average MPG of 27 (Highway), but also has a reported results MPG range of 22 to 32 (Highway).
The truck is still pretty young with only really 68,000 miles on it. I've been fixing it up since i bought with fluid changes and what not and just recently opted to replace the fuel filter.
It turned out that these 1 Generations have it in an odd spot under the intake chamber/manifold. Also intending to clean the throttle body and injectors eventually, I did it all in one shot. I striped the truck of it's intake innards and with great detail and a few cans of throttle body cleaner, carb-cleaner and injector cleaning I cleaned all of the pieces and replaced the gaskets of the: throttle body, intake chamber, intake manifold, fuel rail, injectors, along with replacing the fuel filter.
With use of heavy detergent gasolines like Shell, BP, and Exxon I used to get around 26.5 MPG on the highway, now I get 33.6. That is over the reported results, which were made in the 90's before the Top Tier detergent gasolines. A beautiful change to induce that partially masks the ever increasing prices of fuel in today's market. So, if you are looking for great gas mileage I'd focus on your fuel and air delivery.