99 Silverado Front Axle

I have a 99 ( new style ) silverado 4x4. Early last fall, I noticed the front end was really howling in 4wd. I took a look underneath and
noticed that the driver side axleshaft oil seal was leaking as well as the pinion seal. I changed the axleshaft seal as well as the bearing. When I drained the fluid, I noticed quite a bit of metal on the drain plug. Right before X-mas, I also noticed the output shaft seal on the transfer case was leaking. I had a shop change the pinion seal, TC output shaft seal, as well as the u-joints in the front driveshaft. Unfortunately, it didn't help the howl.
I read in another post that the side bearings have a tendancy to go out in these differentials. I would like to keep this truck for at least 2 more years/45,000 miles. It has 83,000 miles on it.
Anyone else go through this we these trucks? Whats the most economical way to deal with this?
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