RE: Needed help with clunking noise while in 4WD
When you say, "While turning you can hear this grinding in a gear somewhere," are you turning while on a non-slippery surface? Because you shouldn't be in 4WD (especially while turning, and especially if turning hard) unless on a slipperly surface (muddy, icy, snowy, or very wet).
Being in 4WD (especially while turning) while on a non-slippery surface can put extra stress on (or destroy) parts. The reasons being is there has to be some "give" in the system.
About the fluid: check to see if the fluid level is overfilled. The fill plug is located close to the center of the case, about half-way up. I don't remember what size socket it takes, but it was pretty big size. The correct fluid level is just at the bottom of the fill plug. The vent could also be closed/block, or the seals are bad or installed wrong (lip on seal should face interior of case).
Also, the correct fluid is ATF.