Got an 03 Suburban. I have a whine from the front end when I let off the gas in 4WD. I was told it is in the differential. A thing I have noticed is when it is in 2WD and I am pulling into a parking spot, it almost feels like it is in 4WD. Has that hopping feeling when the wheel is turned the whole way. Is this normal?

Gas Mileage was always about 12-13 around town and now it is about 9 mpg. I also changed the passenger side axle seal and has to take off the part of the differential where that weird spacer is and changed the fluid about 5k ago. Is it possible to put the spacer in wrong? I pulled the axle out before I realized you had to take it apart.

The dealership and indy mechanic just say its the differential but i've read so many posts of people fixing this only for it to not be fixed.

 

Possible reasons for that:
You need to adjust the backlash differential;
In the worst case you will have to change the differential bearings and adjust the backlash.
Recently I have done this in my 2003/04 Z71 Suburban because it was presenting a whine between 20 and 40 Mph.