rear end oil

[03F150ESCB-Bob]

truck is an 00 Ranger 3.0 automatic
She has 83K on it im the 2nd owner

Im not sure if it seems like the rear end is a tad loud in it or not and when i had a similar issue with another truck it was low on differential fluid. In any event im sure im going to have to have the rear opened up to inspect whats there. Im wondering if a truck that is used basically as transportation not with heavy loads or for towing in NYC with occasional trips upstate NY if I should be using a synthetic oil in the rear or if i should be using things like Amsoil or a modified oil back there..
Comments? suggestions?

 

[5.0Flareside]

Royal purple synthetic gear oil has Limited Slip additive already in it and is great lube...

thats whats in my rear axle and its extremely quiet...

 

[1985 Ford F-150]

Id just use regular old 90 wt and a limited slip addative if its got it. What I was told is the less addative ya put in it the grabbier the clutches are. Dont know if it wears em down any more though.

 

[LEB Ben]

Where is everyone getting that he has LS? I just read that thing 3 times and didn't see it. Either way, I just grab 80w90 and if I have LS to worry about, grab a $4 bottle of additive.

 

[03F150ESCB-Bob]

thanks for the replies.. im taking it in early next week to have it checked