Posi

How Do I know if I have POSI trac or not. I think that sometimes both tires spin and other times only one tire will spin.

Raise one rear wheel and with the brake off and the transmission in neutral try to turn the wheel. If you can turn it easily it isn't a posi. It should be almost unmovable.

well, what year of truck do you have and do you have the rear axle tag, also if it is the stock trac-lok your trick will not work, but if it is a standard locker, thats the easiest way i know how.