dont bother saying im a noob and should use the searchbar I am way ahead of you and didnt find anything.

now I have a Team Losi XXX-NT sport that I just pulled out of my closet and I think I messed up the differential on it. I loosened the differential screw too much and now the rear wheels are not moving in unison and the slipper doesn't catch on anything it just slips. Any one know how I can get this problem solved?

This isn't really an onroad engine question but it should be pretty easy

The screw in the diff must be all most all the way tight to keep pressure on the large rings and balls in the main gear or else it will spin.

Be sure you didn't lose any of the balls or thrust assembly, look at the pages in this manual from teamlosi.com

XXX-NT Manual

hes right

Maybe you want to try here camp3100 'Losi xxx nt thread'