My avocado tree is dying, It was doing very well for the first year, but then dropped all of its leaves. I figured out that we used the wrong soil. So I re-potted it in a fast draining soil with a 5-5-5 fertilizer. It then dropped its main branch, the other two look like they are about to go. should I just cut it down and let it re-grow better limbs? Thank you!

Condolences. I think you will be very lucky if it comes back. They don't drop their leaves in winter so I doubt it will come back for you. I wouldn't feel to badly about your gardening skill though, I've killed one myself and it was outside in zone 9a. I think they are just touchy when they are young. They grow them here for fruit and I have seen many of small Avocado tree that didn't make it.

As long as the layer under the 'skin' is green, there is hope. Be patient. Don't chalk it up as a lost cause quite yet.