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Eh... well... my favorite way is to stand on the brake and hit the gas to do a burnout... if you leave two marks, one for each tire, you've got Posi, if you leave only one tire mark... you don't. Hehehe! How creative am I? LOL!!
I see that you have an 04 Ram, look in your glove box, on the bottom of the door there will be a sticker that will indicate what gearing your rear end has and if it is an Anti-spin or not.