Hello all, I am new to the group and I have searched a few places trying to find an answer. I recently bought a 99 2500 with a 6.0l Automatic 4L80 Tranny with 180K miles. I am getting a grinding noise when shifting into OD or 4th gear I would assume. Its the only gear that makes a slight noise. My check engine light is on for an O2 sensor that will be replaced this weekend. I have checked the fluid and everything seems fine. Shifts great other than that. Any insight on what it could be. Thank you in advance

 

First you need to check transmission magnet
It's on pan grinding in any great is bad and still fixable as of now but check asap

 

agreed drop the pan and filter check for shavings....I'd also check the tcase fluid

 

Yeah good call grinding nothing to play with I will take clicking pinging piping no whine or grind