Do you have POSI, if not, it will be a lot easier to spin a wheel off the line and bark it going into second, plus there may be a shift kit or something which will also help bark it going into second.
Open your trunk and look at the sticker on the underside of the lid, if it doesn't say G80, you don't have POSI, if it says G80, you do. If you do, when you spin the tires, see if they both spin, and if they both do, see if its an equal amount. If only 1 spins your POSI is burned up and basically an open differential, if 1 spins a lot more than the other its on its last legs, and if they both spin equally its in good condition.
I hope you have POSI and they are both spinning equally. If thats the case it just means you have a good strong motor, which is a good thing.