[ImmaSquashYou]

bad starters can happen all the time. I've changed out 3 starters before i got a good one. 2 from pepboys, and finally gave up and went to napa. That one was good. So unless its brand new, the rebuilt ones can definately still give you problems even if its right out of the box.

How old is ur battery? Your headlights shouldn't dim as you step on the brake lights since your alternator is running. Maybe its your alternator not charging properly. Once the car is running, it should get most of the electrical power from the alternator, something seems fishy there. I might be wrong, but i'll let others correct me if i am.

I had a CPS problem recently with my ford minivan. It was due to the fact i did not use motorcraft spark plug wires. The bosch spark plugs wire i had bought was actually sending a signal through the engine that was getting picked up by the CPS that caused the sensor to be faulty in reality it wasn't. It might not be the case since you've said that you've used quality parts. But then again, i thought bosch was a quality part. Anyways, the CPS might have something to do with ur gas mileage. I suggest to get an actual scanner and scan for all the codes.

as far as your ecu goes, something must be wrong when u swapped since it's not detecting any codes. So at the point that you do get a scanner, you might not even pick up the engine codes cause the ecu is not throwing any.