Hi, 

You can do a small scratch test on the upper trunk and see if it is still green. If it didn't leaf out up there, we can assume that it may have died. In that case, you can prune the dead part out until it is green. The leaf color looks like it is almost fading to the fall color, getting a reddish hue. It could be from transplant stress or failure to establish. 

Sourwoods tend to be notorious for having a difficult time transplanting or getting established. They have a fibrous and deep root system so if it is disturbed sometimes it can cause them to easily die. They are also really sensitive to pollution and urban environments. 

At this rate just monitoring the health, not over or under watering (right now you probably need to water with the dry conditions we have had), and not applying any fertilizers to see if it perks up and can re-grow a main trunk. 

Personally I tried planting one before as well and wasn't successful for an undetermined reason. 

Emily