SLTSIERRA

I have a 2018 GMC Sierra SLT 4x4 with 6.2 and the 8 speed 8L90 transmission. I had the transmission flushed by the dealer at 18,000 miles when the torque converter began to shudder at steady speeds between 45 and 60 miles per hour. It functioned fine for the next 1500 miles or so. However, now at 20,000 miles its not shifting smoothly and yesterday with the transmission cold, I shifted from reverse to drive and the transmission hesitated when I pushed the accelerator. It felt like I was in neutral, the rpms revved before the truck moved. I'm not happy that GM continued to produce a transmission that they knew was defective. I've been a GM man since I was old enough to drive,,,I'm now past 60 and I tell ya, I would not buy a GM product with the 8L90 transmission. If I replace this truck I will research other makes....I'm no longer a proud GM owner.