So I've been fighting nock high for awhile now. Had a newarcher over and was showing him the difference in split and 3 finger andon the 3 under bam...laser arrows!! So iI'm thinking I must be putting pressure on nock in split?? Question do I just shoot underor try to fix form? second is there any reason not to shoot under on a bow tillered for split? I am equally accurate shooting either style and my fletched arrows seem to all fly great but bare shafts are much better with 3 under.

I don't shoot 3 under.  If, like you, I were good at it.  I wouldn't hesitate.  If it ain't broke and it's working well, stick with it.

My guess is that you tend to draw heavy with your index finger, thus 3 under works better.  I draw with my middle finger.
homebru

I think you might be using your arm/shoulder muscles too much when drawing split hence its putting pressure on the index finger to do the work.  Try to relax your hand as much as possible and feel your back (latissmus dorsi, teres major muscles) and core engage into the draw more and it should make you put more pull on the middle and ring fingers- this should help with nock pinch.  Being aware of your hand as a passive hook with your upper arm rotating backward because of your back engagement is what you want.

There's no reason NOT to shoot 3-under if it's working for you.

Usually it causes a bow to shoot louder but that can be fixed too.

Most people that shoot 3-under shoot a bow that's tillered for split. Most people don't have any problems with it either. Usually you'll have to move the string nock higher than when shooting with split finger.

Quick fix to what you see shooting split: tie in a second nocking point below the nock. I did this and once my nock point is set, I no longer see the issue and I've been switching around from split to three under and back a lot lately, so that I can shoot either way on demand.

You might also want to give two under a try

DDave

Thanks all. Dave I tried 2 under but I pull 65#ish and it hurts;-) .
I'm gonna try a second nocking point too. It is louder 3 under how do u quite it down. I have wool puffs and heavy arrows and even the string wraps at grooves.

Three under works, but you may have to tweak the tiller or nock point.  I shoot an ILF so if shooting split fingers, I run the top limb +1'8".  If shooting three under, I run it even tiller.
I too notice a difference in sound if the tiller is not correct for the shooting style.
After several weeks of trying both, I find that I am  more consistent with three under.