Bad case of transplant shock. I'm not going to spend time trying to determine what happened.
If you were my customer, here's my recommendations:
- If you want this tree to be a show piece and dominant feature in your yard, then I would replace it. You can get it to recover, in a few years, you can start the pruning cycles needed to shape it into that showpiece. You have to be prepared to wait and put the effort into the pruning.
- If this tree is just our in the yard and looking to have pecans off it someday, then leave it and baby it.
- Or you could do both, dig this one out, transplant it to a little used corner of your yard and replace it with another tree.
I would suggest if you do get another tree, buy from a nursery rather than HD. I've bought plants there and they do fine, but they are usually things like annuals or roses, stuff that's pretty hardy. If you can find something grown locally better. I think that HD buys from the big wholesale nurseries states away, usually requiring significant shipping which stresses the trees which some (both species and individuals) don't tolerate well.
Local small nurseries will usually have more knowledgeable staff. You can also call some of the larger tree companies ie Bartlett or Davey and ask where they source their planting stock from. I just think you will get a better tree.
I would also suggesr if you are replanting to plant a little earlier in the year, as soon as the last frost is gone. Add some mulch around the base of the tree to keep the roots cooler and hold in the moisture.