I have to agree with frank... I can't tell you the number of times I've seen people with the same issues, always getting good groups, but off sights.. they insist it's the sights, but 99% of the time it's a technique issue...
I know you may be able to shoot other pistols with absolute position, but every gun has a different trigger, different grip, different grip angle, etc... It all has an impact and it doesn't take much to throw things around... Low-Left is one of the most common issues with pistol shooting because it's so very easy to do.
If you want to absolutely prove it one way or another, get some snap caps, a laser, and a friend... Have a friend mix snap caps and real rounds in a mag and give you the pistol so you'll have no idea which rounds are live and which are fake. Now shoot normal and have your friend watch the laser... It doesn't even matter if the laser is sighted, or if you're using it... What your friend is looking for is the laser jerking down and to the left when you fire. Chances are, it will... The great thing about this is, it's a great training aid, between the snap caps and watching the laser yourself it can really train you on good trigger control quick.
Again, I'm not saying this is absolutely your problem... I'm just saying that the odds are much more likely it is, versus the sights, especially after going through two sets.