Iv been chasing this problem since I finished my 4x4 5-speed swap. You guy had given me a few pointers a few months back and iv worked on it off and on. The truck has a one peice shaft and I replaced it with a new shaft made for my truck with a double carded front joint and I put tapered blocks in rear(5degree). The truck has the exact same vibration. Tonight I put the truck on jack stands and ran it up to 55-60. The vibration seems consintrated at transfer case. I dropped the rear shaft and it seemed to go away. Put it back on and it’s back. I put a stethoscope on the transfer case and it didn’t seem to make and abnormal noise and I put it on rear end and it seemed smooth as glass. The entire time I do this I can feel it vibrating. It seems it would be the shaft but it’s been on two dif shafts with two dif setups. The shaft was balanced when I bought it and cost an arm and a leg and didn’t fix it. I thought forsure it was the problem. Is there a chance it could be the transfer case and it just dose it when it has the load of the drive train. I also checked oil in transfer case. It’s at the right level. I didn’t drain it to see if there was any shavings in it. It’s new fluid when I installed the transfer case. Any help would be greatly appreciated. I’m not sure what to do and don’t want to through more money at it and it not fix the prob. Thank you in advance.