So many things can be factors in your new lawn. What type of St Aug and how healthy was it?, how thick the soil was that came with it, and what type of soil, was it grown on? What type of soil do you have that the sod was laid on?
A pic and discription of your issue/s might get us in the ball park of a problem, but short of an actual pro standing on, and probing your lawn in person, I would not spend much time or money doing anything to your lawn besides watering and fertilizing.
That said, most St Aug problems are not enough water, and in new lawns, not enough soil was on the sod (spreading top soil on the bad area is the best bet).
NEVER de-thatch, but verti-slicing is helpful in certain situations, but ONLY if the blades are set very far apart for St Aug
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