Someone smarter than me explain why my truck gets better gas mileage when I have a load in the bed?

Considering figuring out something to add permanently. Suggestions?

I get 1-2 mpg more while having a load.

Thanks

Explain load. Weight? Volume?

Likely due to less drag from bed having something in it. If load is below cab height versus above cab height, it will affect aerodynamics. Less turbulence will increase mileage just a little.

I’d say pay meticulous attention to driving habits and conditions and you will find you don’t.

Possible? maybe, but I’m not betting on it.

You're driving more carefully when you have a load in the bed. Less prone too fast stops or quick acceleration.

Unless the shape of the objects in the bed are improving your aerodynamics it is physically impossible for additional weight to improve your fuel economy. More weight requires more energy to move.

I am thinking it is something like the above people are mentioning like you are driving better with a load. No jackrabbit starts, driving slower, etc.

Other than that could be other variables skewing your conclusions - was it on the exact same route going the same direction? Wind direction and speed the same?

Load has been livestock feed or deer protein. 400-800 lbs

Doesn’t change my driving habits. Not going to blow out or sustain any damage

Thanks