Good Morning;
I'm not a doctor, but I've played one on TV. That said, I do know a little about nerves and anatomy, so here come the questions. Does your finger feel numb and tingly all the time (since you switched from 3-under to split), or is it only when you are shooting and a few minutes after?
If it is still numb and tingly for hours/days after you made the switch, you probably crushed a nerve. This should probably heal up and the normal sensation will return, but it will take a while. You will also probably have to stop shooting or change back to 3-under. This is the more severe possibility.
If it is only numb and tingly after you start shooting, and only remains that way for a few minutes after you stop, then you are cutting off the blood supply to your finger.
Do you use a glove, a tab, or just bare fingers? If it is one of the first two, a thicker one might help. If you are shooting "fingers" (I believe that is the term; I'm new here, so I'm not up on all the lingo yet), this increases the chance that you have done some damage or are cutting off the blood supply. In this case, I would start using one of the above.
Good luck, and let us know how it turns out.
D