Well when my gears first WENT out I took it and the guy knew I had been driving it hard plus it was an OEM part and I had on open diff. Then when the noise started happening that was less then a year later and I told him I had been baby'in it and he had put a LS in. So he replaced the ring and pinion for free. I didn't see any vibe or anything wrong when I just jacked it up but my dad sat in the truck and would give it gas and you could hear a noise when you let off the gas. I'd say probably around 40-50 letting off. IF it is your gears whining they won't leave you stranded or break. They are just going to wear unevenly, and if you really get on it you may break a tooth bc they are wearing unevenly. That is the way it has been explained to me...

 

I had the exact same symptons at highway speeds. Who installed your lift? Do you know if they installed the driveshaft spacer that fits between your driveshaft and the rear differential? Your Kit comes with one but my Rancho kit did not. I had to order one from Fabtech and i installed it and the vibration went away. If you have the spacer installed then i just wasted your time by letting you read this...

 

I did my lift, and what would make it all of a sudden come on? I though about that spacer a while ago.