Two days ago I purchased and planted a 4' tall haas avacado. There was some drooping in most of the leaves at purchase. I dug the hole twice as wide, used tree planting soil, and watered well. I gave it water last night, noticed more drooping. This morning I discovered several curling, browning leaves. It's occurring on full leaves, not simply tips or outer edge. The location gets full sun from 1pm until 7pm, temperature gets into high 90s. What can I do to help it? Thank you

Any newly planted item should be protected from full sun or there will be stress. Can you rig up some temporary shade?

Edited to add:
When asking for assistance it would help to know your growing conditions/climate zone/location to get the best answers.

I most certainly will. Thank you so much for your help.

Others may have suggestions but my dad used to let the garden hose drip, drip, drip all day and all night for about two weeks when a new tree was planted. Just a tiny bit of a drip. Adding some mulch around the base of the tree will help to conserve moisture especially with high temperatures.

Don't know if there is much wind where you are but new trees also need some protection from wind; both sun and wind will dehydrate a newly-planted tree.