Z71 Pick-up. do we think the topper on or off for better gas milage around town.

Around town, the only difference would be the small weight difference. Very small mpg change.

'Around town" doesn’t catch enough wind to make it an issue. Could someone prove you will save a gallon or so a year by having it off? Probably. I presume the topper is there because you keep things out of rain and snow, and get a little security for things left in the box. Leave it on.

Anything that increases weight decreases mileage, but the difference in city driving will be minor. Probably too small to measure.

Agree, only highway speed driving would make a measurable difference. Even then, it would be small.