[KingLT1]

The 8l90 is a solid transmission. Unfortunately, most of the issues are based around the torque converter. The torque converter isn't the transmission. But even then, the issue isn't really the torque converter. It's a combination of incorrect fluid and tuning. GM engineers decided they wanted the transmission to slip in and out of AFM mode so you don't feel it like you could on the A6 in the 5th Camaro. It also helps make power down shifts smoother. Either way it's hard on the converter clutches and the original fluid used would cause the clutches to chatter and you get the shudder and erratic shifting behavior because the transmission locks and unlocks on gear changes.

Before spending thousands, I would pay for a triple flush and have the adaptives reset first. Then reach out to a performance shop and have the transmission tuned. I could do it for you remotely if you had HPtuners.