I am not trying to be rude, but this thread is extremely difficult to follow, but I will try to make a guess here...
First off, I am going to assume you have a V6 as you mention shifting into 4Hi (for future reference it would help to know the Trim, Engine, Year of the vehicle). When you shift the vehicle into 4Hi are you engaging the CDL (Center Differential Lock)?
Can you post a copy of the previous repairs you found? Like a repair order from the dealer or shop? It might help us understand previous repairs done.
~When you say the boot is torn open, is the grease greenish or dark grey?
~Does the vehicle make light growling/grinding noises when turning or driving normally in 2WD? Or is it ONLY in 4WD that you are having this issue?
~Where exactly are you hearing the noise, center of the vehicle, front of the vehicle, ect?
The CV axle could be worn out/damaged and needs to be replaced, the grinding is most noticeable in 4WD because power is being actively applied to the CV axle vs. it just spinning in response to just being pushed along by the rear wheels. You could also have an issue with the ADD not engaging properly and/or damage to the front differential, we need to get some more information and clarity in the matter to properly understand what is going on here.