I do low cadence big gear work so that the weaker leg can't hide.

That's a good idea. I try to focus on working my right leg when I ride, but that only works until I see a squirrel or something else that grabs my attention hahahaha

I suggest you read a Cesar Milan book on how to turn your Dominant leg to a Calm Submissive leg.

Measure both the quad and the calf at the same spot (the widest) on both legs.
If there's a 2 cm difference or more it's often indicative of a problem with neurological impulse/deficit which results in the muscles to the leg being shut down.
But if you're like most, it's just a question of favoring one leg over the other for your entire life. And the issue issue is perpetuated as you pedal or push off or kick a bit harder with the dominant leg in your 3 sports of choice.
If you're in a sport like soccer or Karate where one may utilize one leg preferentially, that can explain the difference. Also, a history of injury to one leg needs to be considered.
Some tips which have already been mentioned include ILT's on the bike, weight training with the legs working independently of each other (not leg extensions and leg curls and the like), as well as leading with your non-dominant side anytime you go up stairs, etc.
If it's taken a lifetime to get them out of balance, you'll never get them perfectly equal. But the above suggestions should help.
Good luck.
--Andrew