With the newer alignment systems (especially Hunter Hawkeye Elite), locking the steering wheel is a thing of the past. You can position the steering wheel where you want it, and roll on with the adjustments.
A few things could cause this.
-They botched the initial measurements
-Incorrect adjustments were made.
-The steering angle sensor/yaw rate sensor did not get reset after adjustments were performed.
If it were my guess, I'd bet money on the last one. They will need an OE capable scan tool with bidirectional control and security gateway bypass capability in order to reset the necessary sensors.
Got a printout of your alignment results before and after?
For the specs, what is the year/model of your truck? 4x4?