Gale - I don't think the alternators bad because there are no other signs of it going, I have a pretty powerful audio system and it doesn't dim the interior or exterior lights at all. And the car always cranks strongly when starting.

Since I bought the 535im it had the stock ecu in it, but when I first got it it pulled noticeably harder than it does now.
I also forgot to mention that after disconnecting sensors the CEL never came on. I know the bulb works because I have done the stomp test before, and it lights up a few seconds every time I start the car
Could this be a sign of a bad ecu?