Think I found out why 3.08\'s and 2.73\'s were so common "How are fuel economy estimates obtained? The fuel economy estimates are based on results of tests required by the U.S. Environmental Protection Agency (EPA). These tests are used to certify that vehicles meet the Federal emissions and fuel economy standards. Manufacturers test pre-production prototypes of the new vehicle models and submit the test results to EPA. EPA re-tests about 10% of vehicle models to confirm manufacturer's results. The vehicles are driven by a professional driver under controlled laboratory conditions, on an instrument similar to a treadmill. These procedures ensure that each vehicle is tested under identical conditions; therefore, the results can be compared with confidence. There are two different fuel economy estimates for each vehicle in the Fuel Economy Guide, one for city driving and one for highway driving. To generate these two estimates, separate tests are used to represent typical everyday driving in a city and in a rural setting. Two kinds of engine starts are used: the cold start, which is similar to starting a car in the morning after it has been parked all night; and the hot start, similar to restarting a vehicle after it has been warmed up, driven, and stopped for a short time. The test used to determine the city fuel economy estimate simulates an 11-mile, stop-and-go trip with an average speed of 20 miles per hour (mph). The trip takes 31 minutes and has 23 stops. About 18 percent of the time is spent idling, as in waiting at traffic lights or in rush hour traffic. The maximum speed is 56 mph. The engine is initially started after being parked overnight. Vehicles are tested at 68 F to 86 F ambient temperature. The test to determine the highway fuel economy estimate represents a mixture of "non-city" driving. Segments corresponding to different kinds of rural roads and interstate highways are included. The test simulates a 10-mile trip and averages 48 mph. The maximum speed is 60 mph. The test is run with the engine warmed up and has little idling time and no stops (except at the end of the test). NOTE: To make the numbers in the Fuel Economy Guide more useful for consumers, EPA adjusts these laboratory test results to account for the difference between controlled laboratory conditions and actual driving on the road. The laboratory fuel economy results are adjusted downward to arrive at the estimates in the Fuel Economy Guide and on the labels seen on new cars, light trucks, and vans. The city estimate is lowered by 10% and the highway estimate by 22% from the laboratory test results. Experience has proven that these adjustments make the mileage estimates in the Fuel Economy Guide correspond more closely to the actual fuel economy realized by the average driver." Our numbers aren't based in the real world So in other words, they put a vehicle on a dyno, crank it up to 55MPH, and check MPG. Then they figure that doesn't simulate real world very good, so they add a certain percentage on. Of course, they make no differentiation based on coefficient of friction, so a Prius and a K5 both have the MPG ratings dropped by the same percent. Thats the gov's info there, so if they left something out that would make more sense, it's their fault. But from what I read there, the makers can easily screw the government/consumers by putting drivetrains in the vehicles that can't possibly be as efficient on the road as in a laboratory because they don't figure in drag for each vehicle. With a K5, drag is huge, so you test a 305 and 700R4 with 3.08 gears, to get the best mileage possible, (helsp the CAFE numbes) without having to factor in how much gas it *actually* takes to propel the vehicle with drag added in. This is probably why my 305/700R4/208/3.08/31 '83 got worse mileage (slightly) on the freeway than my 350/465/3.42/33" '86, and probably holds true for most of the OD equipped 2.73/3.08/3.42 trucks. Each drivetrain combo has to be tested by the EPA, so obviously the 3.73 or 4.10 geared truck will get worse mileage than the 2.73 vehicle, but once you factor in how much drag is on the vehicle, I almost guarantee the 3.73 truck equals out to the "laboratory" 3.08 combo. I tend to fly off the handle in these kinds of issues, anyone want to comment? I can't see anything in that article that takes into account drag though. Hey, put a Nascar vehicle up for testing, I bet based on EPA calculations, top speed is 600MPH!