Transmission shudder?

I changed the fluid twice and added instant shudder fix, but i still have a shudder. It is better than before but shudders at same speed around 30-40 when am letting the RPMs go below 2. No issues at take-off or highway speeds. No slippage or jerking or thuds. It's so annoying. I only driven about 40 miles with insta shudder, do you think it takes time? Also, is it usually the torque converter doing this? And if replaced most likely will fix the issue? I may end up doing that if i have no success with it. No engine or transmission codes per can scan.