if you're driving ther car normal, you shouldn't see a decrease in MPG.
i was getting 26mpg stock, then went to JB4 and still got 26mpg.
now i'm Cobb Stage 1 and will admit i get @ 23-24mpg ONLY BECAUSE the boost comes on a bit quicker and i like feeling it.
when the feeling of the "new tune" goes away, i'll be back at 26mpg.
on the highway nothing changed from stock, to JB4 to Cobb.
IE 392 Challenger...Cobb AP, DCI, ETS, LM Reps....