DP, At this point, I wouldn't recommend changing your limb tiller. You may want to play with your nocking point a little to see if that helps BUT, with your description of the callus on the bottom of your ring finger -- here is what I would look at first.
If you can take a video or second choice a photo of you at full draw, look at the relative height of your string arm elbow. Sounds like it might be a little high. Calluses are indicators that something isn't as good as it should be and especially if the callus is other than on the pad of your finger. Another thing to look at is how much tension you have in the string forearm and wrist. Be sure you are as relaxed as absolutely possible and especially in the wrist. That will allow the weight of the bow to line up your hand and fingers for you. Don't try to do that yourself, let it happen.
As far as high groups are concerned, just start close 5 yards or so and shoot at that distance until you can "see" what is needed to hit the spot. Then back up a little - not more that another 5 yards (less would be better) and shoot at that distance until, again, you start to "see" the alignment needed to hit there. Keep going until you get to distances you want.
Remember that with what ever you finally "label" your aiming system (instinctive, gap, split,etc) that MOST of them will have the arrow tip below the target. If you insist on placing the arrow tip ON the target to be hit, you will always be high inside your point on range.
Yes, it sounds like your occasional high Left is a release issue. We all get that once in a while -- some more than others.
Arne