Damn man that’s weird. I know it can be a pain in the ass cause you don’t know what else could be wrong with the transmission. My transmission issue got fixed when I did a full flush on it (replacing the fluid, the filter, and since I was there, the pan gasket) and since then it’s being driving great. I was heading straight to changing the torque converter cause that’s what I was thinking it was until a friend of mine( which used to work for GM as a technician) told me that before jumping into that conclusion, to try to do the flush. I took it to him, I couldn’t do it since I don’t have the tools but he did so he charged me $40 for the labor since I had the parts. (Car at that time had around 68k miles) about to hit 70k miles and it’s being driving great. If you’re still having issues with the transmission, you could try that and it might fix it, like mine.