Bought new Maghytec cover for rear, quick question

[06SuperDutyF250]

I have an 06 XLT F250 with the Sterling 10.5, Just got the cover, 6 qts of Amsoil 74/140, but want to know if i need XL3 modifier, is there anyway to tell if its limited slip w/o poppin the cover? I know the axle ratio is 3.73 by Oasis report i have...any thoughts, would like to order tonight thanks

[nghtrgr]

I used Valvoline which clearly stated no friction modifier required unless chatter? occurred. Give Amsoil website a look, it should say whether or not you need to add it.