The op planetary looks like a thrust bearing failure as mentioned. I had a similar situation in my 97 Yukon. I bought a video from technical video and the atsm manual and all the appropriate tools and rebuilt mine. Absolutely the most rewarding thing I've done. I did the Beast sun shell, 5 gear plantary update, corvette servos, kevlar band, valve body updates, extra clutches . Thing hits a hard second. Honestly, the parts are so cheap to go and do all these updates while you're in there. I just watched the video on the computer, play and pause all the way thru, air tested all the pistons before moving to the next stage. Trans is flawless. I probably have $700 into parts including a new convertor. That doesn't include the price for the tools, I even got the bench mount to hang it off your work surface. My dad always pressured me to rebuilt an auto, I was always reluctant with the hydraulic voodoo inside. But, it was really easy. I'm sure by looking at the clutches in mine that a trans shop would roll the dice on replacing all the stuff I did. I wanted to know what was all going in. Not saying trans shops are shady, but do you really know what they're putting in?