it's like a highway gear and tight converter, exposes every imperfection of the carb (in your case carbs). If you roll along at 3000 rpms in first and mash it and it seems ok, that's just masking the issue. 3500 stall converters and 4.11 gears do the same for an automatic. If you stay with it, you'll tune the hesitation out, even at a low rpm. That's when you know it's set up right. Even though it's different, my car was kind of the same with the factory converter, 2.45 gears, and getting the 750 Double pumper to work from a dead idle mash. I got it with zero hesitation from a low idle mash, and you will too. Now, with 2.94's, consistent 1.8's. Don't hide it with rpm's and the clutch. Stay at it till it works. Sorry I don't have any suggestions for you as you are trying one thing after another.