There actually isn't an lock tab on the transmission side and that should simply slide off. The outer tab you pried with knife actually is what you are supposed to push in with your thumb to release it from the transmission connector.
The way this stupid thing is supposed to work, is the tab slides on the OUTSIDE of the snap when you install it, but to release it, the lock has to slide on the INSIDE of the snap.
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I have never seen a connector style like this anywhere in my life and I suspect to ford engineers just got really really pissed for some reason. Later E4ODs elimitate this style of connector to favor the more proper thumb tab release that most vehicle connectors have today (the MPLS should have that style of connector).