I’m not even going to bother refuting the first half of your post, because I agree, there are a ton of variables. I know you own an e39, which arguably has some of the worst gas mileage of any (modern) BMW’s currently on the road. The auto vs manual does make a ton of difference due to gearing and drivetrain loss. Average BMW drivetrain loss for a manual is around 12-14% whereas the auto is closer to 18%, combined with the differences in gearing, the auto gets SIGNIFICANTLY worse gas mileage. As for the diesel truck, it’s not hard to get 15mpg in them, hell driving like a grandma the last time I was driving one I only got 19-22.
Of course no hard feelings, this is the internet afterall and I know you’re not as retarded as the OP.