I'm no expert, but experienced something similar: The car felt like a manual transmission with the clutch pushed in part way until the stall speed was reached. Anything below that and my throttle felt "spongy". In cases where I spent some time below the stall and then mashed the throttle, the engine would rev and then it would feel like I "Popped the clutch" when the torque converter decided to catch.

I went to several tranny shops who suggested swapping to a lower stall converter.

A random person at a car show explained to me that the converter was "draining" faster than the pump was filling it when below stall. The "Laziness" was a result of the torque converter filling first and then doing what its intended to do. I took my car to a knowledgeable shop and mentioned this. They installed some sort of "Block-off plate" in the valve body. (This is what I was told).

Now the car acts like it was supposed to: No more hesitation, No more spongy throttle.

My