today i heard that bad brakes could cause bad gas mileage...is this tru or just a rumor?

Only if they stick and drag when your foot is not on the brake pedal.

Gas milage has alot to do with the way you drive. Tire pressure etc etc etc I like those new mazda engines(3 and 6 class), been thinking about a swap into my Heep. Just for the onroad gas savings. I am not sure if it would be any good offroad, I would just rev the BEEP out of it. No different then the Jeep 4cyl I bet.