Ok guys i recently changed the rear diff oil, used amsoil 75w140 which my 99 5.4L specifies to use about 2 months ago and now i am getting this real loud squeak it seems every rotation of the tires... I checked the brakes to see if it was something there and everything looks good, could it be a problem with my rear end???

 

It could be an axle bearing or U-joint. Can you pin-point the location of the squeek by puting the truck on jack stands and turning the drivetrain over?

 

i was going to try that but i talked to a mechanic i know and he said more than likely it is the u joint....