You guys ever do 'em? burned the tire(s) a little bit yesterday, dropped the clutch on asphalt and revved it to about 6500 without brakes and only left one track.
You need a rebuild of your diff. There are methods for rebuilding the trac-loc in the 8.8 to add more clutch discs and set the breakaway torque spec properly. Sean Hyland's book on 4.6 Mystangs has a section on this.
I had my trac-loc rebuilt about 4 years ago now and it lays two SOLID black strips when the tires roast.