I tried like you said Y.J. and it didn't seem to be slipping/grinding in 4H. However, when going 40-55mph range in 4H can hear a whining sound I never heard before that sounds like it's coming from the same area/hub location. Took it into local Ford dealer and they gave me the usual, "We can't get it to replicate the sound you say it's making... Technician notes no unusual 4x4 sound..." So, I guess I'll wait and see if it breaks. Hate that feeling. Hope warranty covers the tow from the mountains! Probably would be cheaper for them to replace it now. Oh well.