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I just changed mine. I went with the Amsoil 75-90 extreme duty. I didn't use any friction modifier and my LS is still smooth as silk. I would go with the Amsoil.
I wonder why the manual changed, given the relative few differences between the OBS and NBS trucks. The 99+ service manual cals for synthetic 75w-140. I currently run the Amsoil in mine, but it's getting a bit chattery of late. It's almost due a fluid change so I'll probably go with the Red Line heavy shcockproof, or Royal Purple this next go around.
The 75w-90 is easier to find if that has any bearing on your desicion....nobody local carries the -140.
Rezvani's Latest Post-Apocalytic Monster Is a Ford F-150 Raptor Underneath
Slideshow: Called the Fortress, the 850-horsepower pickup combines Raptor underpinnings with military-inspired features, survival equipment, and a starting price of $285,000.
Rear diff fluid
