2006 CM870 vibration in floor 6th gear

[Pete379]

Is it a steady vibration or does it pulsate. The reason I ask is that I’ve noticed all sorts of issues over the years both vibrations and grinding that could be attributed to ride height on peterbilts with air suspension. I had an 07 that would vibrate in the cab under load and only in high range it turned out to be running too high I had to adjust the ride height valve. It’s worth a shot to take a look...