what is the button on the automatic trans shifter thats say's hold this is found under the shifter nobb

That is to defeat the overdrive/lockup. Most people in most driving situations would just leave it alone.

No that hold button is actually for the auto-box to change down without using the kick down. This also saves more fuel. The longer u keep it in hold the more rev's u gain in the gear u are in, and u can red line it before pressing it again to release. When u press it again it will change to the next gear up.

i just got a mx-6 1993 we changed the auto fluid as it was going but as soon as you put your foot down it would slow down , we done this 3 times which it seems a whole lot better but now when you take off it revs then takes off , would yous have a clue what makes it do that?