The spacers in the front are still on. They are 2 1/2. The spacers in the back are no longer there, they were wheel spacers. It is at stock height, so I dont think that would affect it. As for the suspension, its stock except for the front level kit. I might put a 1/2in spacer in the center carrier bearing see if that helps?

 

UPDATE****** The vibration turned out to be two of the wheels on the truck. One was on the front right and other was rear right outer. Replace both with some used ones that were not bent and truck is back to being smooth. I was still gonna add the spacers to the center of carrier bearing as was suggested and will post an update once thats on. Thanks again for all the help!

 

Glad you figured it out!!! I bet you are happy to have your smooth truck back!

 

Good that you got it fixed, but you said this vibration was with 2 different sets of wheels but your above statement pretty much isolates the issue to the rear driveline angle, especially with a susp lift on a 3500. Ive had bent rims before on my Charger on 20s and the vibration did not come and go with certain speeds. It just vibrated through the steering wheel and chassis constantly, at highway speeds.

I never felt I had any issues with the 2 pc driveshaft on my stock ht 2500 Mega 4wd until I had a u joint start to go out. Squeaky, vibration at low speeds when accelerating. Isolated it to a bad u joint, and the carrier bearing on the center support still appeared to be competent.
So I ended up just buying a 1 piece driveshaft at the dealer because I didn't want to fick around with rebuilding the driveshaft up in AK where I had limited tools and no shop.
The difference was night and day smoother compared to the 2 piece even when it was "good".

 

I think it was a combination of things. It felt like a hop and vibration all in one. The entire cab would hop. I replaced the front wheel bearings and an axle shaft that had play at the ujoint. That took the hop away, but still had a vibration. Had someone follow me to isolate the side or if in the front or the rear, and they told me the front looked good but the bed was hopping, sorta like driving down a rough dirt road, but not all the time. I jacked it up the rear and noticed the wheel was bent, replace it and now its smooth. Lets see how long this lasts? I do plan on putting a spacer on the center bearing, see what that does. But for now, its smooth.

 

Glad you figured it out, I had the 70mph when i bought my truck new in 04, dealer thought it was in the front end, I knew it was notbut they could not figure it out. I have installed many drive shafts working for a major truck manufacturer, and I thought the angle from the center carrier bearing to the rear end was to much,and it only makes it worse under acceleration. I spaced my center carrier bearing downabout an inch (4 pieces of 1/4inch flat stock), and the vibration is gone. I had posted some pictures on here years ago when I did this under " 70 mph vibe" I think. You may be able to do a search and find i. I hope this helps.. I found it ( Fixed 99% of vibe problem) post #11 has pictures.