Dave H

Be sure you are keeping it tight, no slip. The slipper should always slip first.
Check the setting on a new diff after running few minutes, they bed in a little. Some guys hold one wheel, the other in the air, and run the motor part speed for a few minutes for break in.

Also be careful that you are not overtightening the diff, that can put spots in the rings & balls. Take your time tightening it, check it, tighten a little at a time. Perhaps a 1/8 of a turn at a time. Replace the lock nut every couple builds, after a while they won't hold setting.

Tighten the slipper more than normal, lock both wheels, then turn the spur gear with your thumb. Should be pretty hard to turn, and the slipper should slip. Then loosen the slipper to suit.

The stock AE greases are top notch, use them. Not a lot of the clear silicone on the diff balls, a dab on each ball on each side, use a lot of the black on the thrust.

Go back through your manuals, make sure everything is correct. I haven't ran a AE tranny in a while, but when I did their manuals were quite good on diff building.

I know it's tough at first, but you develop a feel for it after a while. Done right they should go quite a ways, I run them for months typically.

Somebody at your track should be able to help as well. Good luck.