For the last few weeks I've been driving my truck (see sig) in D instead of OD around town and it appears I'm getting better gas mileage when comparing my trip meter to the gas gauge. Usually when my trip meter hits 150 I have half a tank, but today I noticed the trip meter at 155 and the gas gauge is half way between 1/2 and 3/4. That's a lot when you figure it has a 30 gallon gas tank. In OD around 37 mph it runs 1050 rpm while in D at 37 its 1350 rpm. So lugging the engine in OD at lower speeds must use more gas.