You should swap the front tires left to right. And see IF the pull changes. IF it doesn't... swap the rear left to right. See IF that changes the pull. Chances are you have more than one bad tire.
Perhaps your frame is bent or the alignment just off. YES, even with two shops just doing an alignment for you. You know the term... "set the toe and let her go"!!!
It happens a lot.
Ask around in your area... I am sure their is a shop known to cure problem cars like yours. You could have a bent shock or suspension part. Especially since your lowered.
But for now... you can change/swap your tires left to right to figure out IF its a bad tire or not. I assume you have checked your tire pressures right?
PS: Post both alignment specs. They did give you those right>?