The center diff is unloading the extra rpm to the front hersavage, you need thicker oil to make use of the extra power. Try something 100K or more, some I know are using 300k even 500k
My mt4 has developed a strange noise under hard acceleration and I just can't seem to find out what it is. I've inspected all diffs and everything looks good. My hub carrier bearings are quite rough, could this be the source of the noise? My wheel hex'es are a bit stripped too. I really hope its those bearings as I have a new set on the way.