downshift vs neutral

[Lirueil]

what would give better gas mileage between downshifting or putting it into neutral

Not sure it matters in terms of MPG, but down shifting is good for slowing down where as neutral is not.

what would you recommend as a top speed.

I'm pretty sure the Aveo user's manual states that 55mph is ideal for best MPG, at least for my 2007. Not sure what other model year manuals state.

also what would be the lowest rpm i should shift? i use to shift at 3000, now around 2000 is this good or bad

My best MPG has resulted in shifts at 1.75k - 2k rpm, but due to comfort I usually shift between 2.25k -2.75k rpm.