You have several things to deal with here. If in fact you trust this reputable shop. I assume this is a lifted truck. If so, here are your scenarios.
1. The steering wheel is only off center when you are in the left lane because of the crowning of the road. Your alignment is fine. You have to hold your steering wheel to the right to stay straight.
2. Your reputable shop does not know how to complete an alignment. Centering the steering wheel is a part of this process. It is also possible that their machine has not been calibrated recently. If they have an appropriate Hunter machine that is less than 10 years old, calibration is a piece of cake.
To actually answer your question, you can center your steering wheel by adjusting both tie rods. You'll have to be very meticulous with your measurements, as they need to be dead even left and right. Otherwise, you'll change your toe settings.
But in reality, you should determine which scenario you're dealing with. You should not have do your own steering wheel centering.
Do you have the alignment specs available?