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The axle oscillation bushings was a good call, most people miss that as a source of noise.
Another issue could be the center drive shaft. This joint should be replaced every 10,000 hours or earlier for severe conditions. Using chains are mismatched tire will cause excessive strain on the slip joint.
This will also cause a slight vibration when turning.
Don't forget to inspect all engine and transmission mounts. If they get oil in them the rubber will deteriorate and allow the engine to rock around too much. This can also add strain on the drive shafts.
Inspect the slip yokes in the axles, the splines here can wear too. Excessive wear can cause them to strip out This is usually just the yoke and not the axle pinion that wears.
Sometimes it can be the cylinders sliding side to side when the load is light. I have even had a couple of loose cab mounts make noise.
Loose steering cylinders will also slap in the pin mounts. Not many use the tapered pins and straight pin will make noise when the bore is worn.
I can't think of anything else. Let me know if you need more information on any of these ideas. Please post your serial number if you do need help.