Thank you for your suggestions and information, I will most definitely put it into practice! I've done well about keeping my use of the 4x4 feature to a minimal and I only engage it when necessary as you suggested. I was told to run the vehicle in reverse for at least one complete tire rotation after disengaging the 4x4 function, so I've been doing that but I hadn't ever heard to engage the 4x4 feature simply for the purpose of keeping components lubed and preventing stagnation/drying of those critical components; I will definitely make it a point to begin doing as you've suggested - occasionally run the vehicle in 4wd on long straight lengths of road with no turns.
The main problem I was experiencing noise from ended up being that the far front U-joint on the drive/propeller shaft was blown out and needed replacing. I finally got a new u-joint installed yesterday and upon test driving the vehicle, I did not experience any of the noises/symptoms that prompted my post of this topic and all the work I've done on the vehicle in recent weeks. However, I'm now curious about something after getting the drive/propeller shaft installed with the new u-joint. I noticed that there is a small amount of play or slop at the far front union where the drive shaft yoke connects to the splines of the bevel gear at the gear box. Do you know if this is normal? I inspected the splines of the bevel gear and the corresponding splines on the yoke of the drive shaft and did not see any obvious signs of wear that might warrant replacing the components so I'm assuming this play I'm referring to is normal. What are your thoughts about that? I don't hear any abnormal or concerning noise coming from that location when driving the vehicle so I'm hoping it's nothing to worry about.
Again, thank you for your response and suggestions, it is greatly appreciated!