Driveway sinks

older home, originally 1 car driveway (concrete), widened on both sides about 15 yrs ago. The drive has sunk in a few places, especially on one side of add on...can this be fixed by adding about 2 in on top or will the whole drive need to be yanked up Texas

The situation you describe is usually related to soil settlement. Most likely, the soil under the new drive was not compacted properly before construction. Since that driveway has been in service for 15 years, it is likely that the soil reached it's needed compaction by now and will not settle further under these loads. If that is the case, leaving the original drive there to serve as a solid base would be the best bet. Two inch topping is a little thin, but may work if the base is stable enough. Make sure that the new topping is NOT bonded to the old, and that you provide cut (or formed) joints at no more than 10' distance. Preferably, match the joints already in the existing slab. I am assuming you are going to place new concrete that is at least 2 inches thick. If you are planning to "feather" it down at the edges the thin areas will likely break under load.