I installed some 4.88 gears in my truck with 3rd members out of a 4-runner and I have a couple of questions. I think my new rear diff is a limited slip if you drive it in the air and both tires spin but if you shut the truck off and spin one tire by hand the other tire spins the other direction doesn't that mean that it's a limited slip? If so should I put in a limited slip additive like in my newer truck? and also after installing my gears it seems that my speedo reads the correct speed with 33" tires is that true? Sorry for the newbie questions

Thanks,
Brian