I was actually in the same scenario as you except my magnet was caked with sludge and shavings was even having the same symptoms after and realized my trans was running pretty hot so I installed a huge trans cooler and a year after that I did a shift kit and the symptom has gotten better with both installs. still does a hard shift that makes my girlfriend jump if you stuck in traffic every now and then but im pushing about 270 to the wheels and its holding up also had to replace some leaking lines before the trans cooler that may be your problem as well those lines are sneaky when they leak haha then next thing you know you cant accelerate when turning left.every time I put in the acdelco dex 6 full synthetic as well ive been told this was the best so I went with it
