hmm... Jason, your problem is summed up like this i think: shooting low and left consistently when shooting semi-auto handgun.
here's what i think is happening when you shoot that is causing you to shoot low and left.
as you are pressing the trigger rearward, your mind and body are unconsciously anticipating the resulting recoil that will happen when the hammer falls. what the body usually does is try and control the recoil that will be going up by either pulling down and trying to control the recoil or squeeze the gun REALLY hard to keep the gun from recoiling upward.
it seems that you are not that recoil sensitive as you seem to be shooting some large caliber handguns, so to me, that would eliminate pulling down on the handgun to control the recoil. i think that you are squeezing the handgun you are shooting too hard... in what is sometimes called a 'death grip'. have someone watch your strong hand as it grips and shoots your handguns. if your knuckles turn 'white' then you are gripping the gun to hard resulting in the low and left shot placement. you can even tell that this will happen by taking a shooting grip and squeezing the strong hand hard. you will notice your hand will naturally point low and left from where you were initially pointing when gripping hard.
to correct the low and left problem, you have to relax your strong (gun) hand and squeeze more with your support hand. this will not cause 'limp wrist' malfunctions as you really do have enough grip on the gun to have the recoil impulse work it's magic on the gun. the previous post of relaxing your pinky finger is excellent advice too. i would go one more finger and say to relax your ring finger too. remember, the only thing that should be moving in the shooting hand is the trigger finger. you must relax the rest of your grip, which includes your forearms. if your forearm is tight and hard, then you are not relaxing enough. squeeze more with your support hand, and relax your gun hand.
whether you shoot both thumbs high and pointing forward or thumbs locked crossed, it won't matter much. i will say it is easier for most people to shoot thumbs locked crossed as they can feel the support hand squeezing more and it is easier for the mind to relax the gun hand as it knows there is sufficient grip on the gun.
once you understand the mechanics of why you are shooting low and left, it then becomes a mind game. you have to tell yourself that to focus on something else other than the recoil... the mind does one thing superbly, but two things horribly. we do not multi task well at all, so if we say in our head or out loud, 'front sight, front sight, front sight...' as we use steady pressure on the trigger, the mind tends to be distracted from concentrating on the upcoming recoil and the body doesn't tense up and 'death grip' the gun just before the gun goes off. you replace 'front sight' with 'relax, relax, relax', or whatever mantra you want... just keep it simple.
the dummy round drill is a good one too. in a semi-auto, it will be a tap and rack drill. load 3-4 dummy rounds out of 10 rounds loaded into the magazine. if you don't concentrate on the recoil, you will have a steady gun that remains on point of aim.
having too much trigger finger on the trigger usually results in POI that is left of the POA, but not down. i don't think you have this problem.
another thing to do is not look at your target after you have shot. focus on your front sight for 3-5 shots and then look where you are impacting. this keeps you from chasing your rounds and keeps your eyes from getting tired.
anyhoo, i think i wrote too much... hope you were able to find something in my monologue to help you shoot straight.
