Wait a minute dude... before you go messing with everything under the sun do you mean you know your spring is messed up or cracked? If so, stop everything and fix that. Damn good bet that could be the issue. And even if it isn't, a cracked/broken/damaged/sagging/different spring will easily cause instability in the drive and unwanted control characteristics during an emergency maneuver. If you have a kid on the way... better get that done!

 

Hi. Was there any resolution to this?

I have the same exact issue. Before my truck with a 3" lift was smooth as glass. The centering ball on my GBR HD front shaft broke one day and made an awful crunch sound. It didn't separate though. While that was out for repair I decided to add GBR 4.43 diffs with Detroit Tru tracs.

When I got the truck back it had the high frequency vibration at 70 mph.

Took the front shaft out and locked the diff and it's smooth as glass. I had a reputable shop balance the shaft twice. They swear it's good. I even went as far as getting another brand new shaft to try. Same issue.

So far I have changed:

transfer case output bearing
Transfer case front flange
Front diff flange

Truck has 69k miles and engine and trans mounts look new.

Could it be the Gbr front diff?

Edit: I also swapped out front rh hub with one from eBay while I had the diffs swapped to 4.43. Has anyone had quality issues with random hubs off eBay?

HELP

 

I'd lock the diff and remove the remove the rear shaft and only run the front - to rule out the rear shaft. Tires balanced? Ebay hubs can be ok, i'm on 30k+ on a set i got from ebay and they are holding up. Does the vibration still happen when at speed but the truck in neutral?

 

It's not the rear shaft. I had the ab conversion shaft on there and it was smooth. Took it off and swapped my original rear shaft on. Still smooth.

Does not feel like tire issue. It's a high frequency buzzing/vibration like I'm driving over rumble strips.

Vibration still happens with truck in neutral. Steering wheel does not shimmy like when a tire is out of balance.

 

Maybe I will try this bc I haven't ran in this actual configuration. I'm just curious as why it would be smooth with the front shaft out if it were a bad rear shaft or rear transfer case bearing. I'm pulling my hair out on this one.