looking for some ideas here.

I've got 38,000 miles on my 05 4x4 quad cab w/nv5600 6 speed. I'm getting heavy pulsing or shudder progressively becoming worse. This happens under 25 mph, usually in 1st and 2nd gear, in a straight direction. I've removed the rear drive shaft and took it to a specialized driveline shop, it came back with no defects noted. I had them replace the carrier bearing just as good measure. Still pulsing... I've jacked the front end up and checked for binding, everything seems smooth. I also disconnect the front shaft and the u-joints are not binding or seized.

I really don't think its a clutch issue, it has never slipped once above 25 mph. Just for kicks, I engaged 4x4 high and the vibration reduced to only a very slight vibration.

any ideas?

 

Did you check the front drive shaft?

 

i removed the transfer case side of the shaft it it seems smooth without any binding

 

I have a 2nd gen and mine is an auto trans so this same scenario may not apply to you but if it is it is cheap and fairly easy. After having my trans done I had a real problem with what you describe and also at moderate speeds (50-60mph) under heavy acceleration pulling a trailer. I called the trans shop to ask them what the heck it never did it before the rebuiild. He suggested that I shim/spacer the center carrier bearing down. He said start with 1/2 an inch and go from there until resolved. I did that and 1/2 inch worked for me.

 

i just added a 1/2" shim (plywood for now) and in 4x4 the the vibraton is completely gone. In 2wd it still vibrates, I'd say 50% better. I'd like to try another 1/2". How much shim can I add safely on a stock truck? The carrier bearing i had installed is a different design, it's rounded on the bottom. I'm wondering now if the new carrier sits closer to the mount than the stock one did. I don't have the old part....darn.

 

I think he had told me he had gone well over an inch before but start at 1/2 then add a 1/4 at a time. The only issue with going too far is if the driveshaft slides up the splines too far and bottoms out. It wouldnt just sitting there but possibly during max suspension compression so you dont just want to add 2 inches and call it good You might try 3/4 inch see what happens then go to 1 inch if needed.
And as you stated plywood will work for a test but I would sure switch to something more substantial once you get the desired level such as bar stock or something solid and weatherproof.