10 % drop in mileage
I first noticed about a 10% drop after the first attempt at reprogramming. It took the dealer two tries.... I used to reliably get 34mph on flat highway at 70mph.. I am lucky to get above 30 now. City driving (without too much traffic) was giving 28-29 mpg but now it is 23-25 mpg. Repeated inquiries to the dealer service department have only netted "the engining is performing to spec's" response.