I have been shooting split finger for more than 12 years I have switched to 3 under and my question is. Is the greatest amount of finger pressure on the string supposed to come from my index finger, or can I still use my middle finger as I had with split?

I try to keep most of the pressure on my middle finger.  3 under solves a lot of problems, but it creates some too.  Something I've just began to pay attention to is the tendency of my ring finger to drag on the string.  Because of the string angles, I think this is more of a problem with 3 under than split fingers.

After 20 years of shooting with a glove, I've started experimenting with a tab, mainly because all the best shooters seem to use tabs rather than gloves, and I wondered why.  My shooting has improved in the short time I've been using a tab, and my thought is that my middle finger and ring finger come off the string more as a unit with a tab rather than individually with a glove, which makes me have a cleaner release.

It will take more experimentation before I convince myself to use a tab, since the tab feels awkward to me and I feel like I'm fumbling around when I load arrows.  But if I continue to shoot better, I will probably get used to those things.

I agree with you on the tab I can't seem to get used to it. I have shoot with a glove since '87 when I shot a wheel bow. I will keep trying though I also wonder about the cold Wisconsin temps and that tab how would I ever shoot with my fingers frozen off. LOL

I had to look at my fingers for this one.  The heaviest callus is on my middle finger but I also have one on the outside of my ring finger.

CJ I should assume you shoot 3 under ??