2nd Gen Non-Engine/Transmission Vibration

[Neibe]

I've got a vibration when I'm in 4 wheel drive between 30 -45 mph. I can fell it a little bit in 2 wheel drive but more pronounced in 4. I'm thinking axle shaft u-joints got 113,000 on truck but before I tear it all apart I was looking for your ideas. Just had new ball joints put on last summer and I wanted the shop to replace the u-joints while it was apart but they said they were still good that was at about 100,000.