(I haven't, by the way, been driving as though I was in Total Economy Run. My 100,000 miles include 2,000 pulling a caravan.)
Speaking is more informal than writing, and this sentence is more like speaking -- very informal.
I have not, you know, driven this car in a way that gives me the most miles per gallon of gas. I drove 2,000 of the 100,000 with a heavy trailer attached to the car.
The speaker is suggesting that pulling a heavy trailer will give you lower miles per gallon of gas.
Student or Learner