New rubber brake hoses...
 

So I replaced the rubber brake hoses on my rolling couch since one of them was looking a bit leaky. All the hoses were soft as spaghetti, and likely degrading inside. Turns out one of them was dragging just a little, as my instant MPG on the ScanGauge went up about 1 mpg on the highway. The tank after replacing them was better than the previous tanks by about 1 mpg or so, even with colder temperatures and snow tires. Can't complain when maintenance boosts FE! :)

"...dragging just a little..." could refer to either:

• disc caliper that wasn't retracting.
...or...
• drum shoe that wasn't retracting.

...which?

I think a caliper and a wheel cylinder. The drums were always warm upon getting back from driving around my little town. And, one front wheel was always dustier than the other, confirmed when the pads on that side were more worn.

The car coasts better down hills better, too. On hills where I lost speed before, the car now holds a steady speed. Something freed up, the car stops on a dime, and I'm happy.

Either way, it's the same physical defect manifesting itself. The rubber inside the brake lines degrades and swells up until the passage through the line is actually pinched closed. Stepping on the brake pedal generates hundreds to thousands of PSI of pressure, so liquid can still push past the pinched area to the caliper or wheel cylinder, resulting in normal brake operation. However, when the pedal is released fluid only flows back until pressure at the caliper/wheel cylinder drops to the point where it matches the restriction that the collapsed hose presents. That means a certain level of residual pressure being applied to the brake, even when the pedal is released.