Clunking from the front?

I have a '89 limited, with a NP242 and I believe dana 30 diffs. However, I have a problem and I cant tell what it is and I have been reading posts trying to figure out if anyone has had a similar problem.
Whenever I have my car in one of my 4x4 modes (either part-time or full time), I hear clunking sounds when I am putting my jeep under stress (ie. backing up, going up grades, turning, or accelerating over 2250 RPMs). The sound seems to be coming from the front, and not the transfer case, but I could be wrong. The sound also has a nasty vibration that comes with it causing the whole car to shake. I have riden in a different jeep when its chain slipped and the sound 'came from the transfer case' so to speak not the front.
I currently think that the problem lies in my front U-Joints, and I am in the process of replacing every U-Joint with the exception of the double cardan joint on my drive shaft, which appears to be in perfect order. I was wondering if anyone else had any ideas about what this could be otherwise?

Whenever I have my car in one of my 4x4 modes (either part-time or full time), I hear clunking sounds when I am putting my jeep under stress (ie. backing up, going up grades, turning, or accelerating over 2250 RPMs).

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Pull the cover and make sure none of the teeth in your front diff are chipped. Check u-joints and also make sure the front shocks are secure.

Had one that sounds like that exactly... driver side motor mount!