GM explains year-over-year MPG shifts, expected to draw up compensation plans for owners

"New emissions-related hardware in the [Enclave, Traverse and Acadia] required new emissions testing for these vehicles," said GM spokesman Nick Richards in a statement. "The fuel economy data from these tests were not captured in calculations for EPA fuel economy levels for the 2016 model year Traverse, Acadia and Enclave (causing 2016 model year fuel economy numbers to be overstated)."

GM claims the error was picked up as engineers worked on next year's window stickers, at which point GM alerted the EPA and started making the switch to the proper, albeit lower numbers. Vehicles with the improper figures on their window stickers cannot be sold until the correct ones are applied.

Once that's done, it's time to focus on making things right for the customers who bought vehicles with incorrect fuel-economy numbers. Reuters reports that GM will reportedly compensate some 130,000 owners. This follows in the footsteps of Hyundai/Kia and Ford, both of which have had to pony up in the past for overstating fuel economy on their window stickers.