Hello I have a problem. I have a 1996 sts 158,000 miles that was or is having shifting problems with no codes showing up. It started out not being able to stay in drive and the list 3rd and now it shifts spastic. Fluid level is good and doesn't smell burnt. I decided to go ahead and change fluid and filter. Dropped the pan to find white plastic shavings and chunks in the pan. Any help would be appreciated. Thanks