I just found out today that you can shift from 1st to 2nd, 2nd to drive.. and so on without pressing in the shift button. Is it healthy to do this while driving at say 55(D->OD)? Or is it better to just press the button and shift.

It is just fine to up shift without using the button. The only time you should have to push the button is when shifting out of park, going reverse and drive or down shifting. Just out of curiosity do you shift yourself all of the time or do you just put in in D and let the car decide when to change gears?

I leave the car in OD most of the time. When I know I am going to have to pass someone I'll drop it down to D (3rd gear) so I get a clean kickdown.

I usually just pop it into drive for most driving. If im going on a road that I know is flat or mostly downhill, ill pop it into overdrive. Will using overdrive all the time save you gas mileage? Is Drive the best to pass with?

Using OD will save gas especially on highway driving. If it is mostly city driving it won't make much of a difference. Having it in drive does make it a little easier to pass quickly. I usually just leave it in OD and have had no problem getting around cars quickly.

Yes, if you're babying it and going over 30mph.