I put a 3" lift in and when i am going passed 40mph with my foot just resting on the gas peddle there is a horrible grinding noise underneath and i cant see what it is.

 

I only went up 2" and get a grinding sound when I let off the gas. Never heard of it reading walkthroughs etc. here. I posted in a nother thread, where the only suggestion was something about the slip yoke. I have a 2001 and the rubber boot kind, so I can't see what's going on under there. Good luck, and post if you figure this out.